How do you know it wasn't done by witchcraft?

I used to say, most sickness comes on a person due to their sins, but this past year has opened up a new area of understanding for me.
In my earlier years, I would hear a voice tell me certain people, actually it was always women, were witches. I didn't think anything of it at the time, but just avoided contact with them, as I believed they were bad people and I shouldn't associate with them. I was also cautious around the person I was told was a witch.
I have a number of stories I could tell about someone having a gift, and another person would comment about that gift, whether it was how smart the person was how beautiful their hair, skin, or face was, after the comment, something would happen that caused the person to lose the very thing the other person commented on, and the one who commented on that said gift, received the very thing they noticed and commented on, and the person that had the gift, they received what the other person had. Just like Satan received Adam's power and authority, which was a blessing of and from God, and Adam received the devil's curse.
As a short example, my wife's brother, many years ago, was a very smart young man in high School, until one of his friends mentioned how smart he was. Her brother was acing all the tests with no problem and his friend was struggling and was not very smart at all. Until she noticed the reversal. How his friend was starting to Ace the tests and her brother was failing in classes now. So what happened? How did her brother lose his intelligence, so to speak, and his friend gets so smart so quickly?
Was it witchcraft?

... As a short example, my wife's brother, many years ago, was a very smart young man in high School, until one of his friends mentioned how smart he was. Her brother was acing all the tests with no problem and his friend was struggling and was not very smart at all. Until she noticed the reversal. How his friend was starting to Ace the tests and her brother was failing in classes now. So what happened? How did her brother lose his intelligence, so to speak, and his friend gets so smart so quickly?
Was it witchcraft?

I used to say, most sickness comes on a person due to their sins, but this past year has opened up a new area of understanding for me.
In my earlier years, I would hear a voice tell me certain people, actually it was always women, were witches. I didn't think anything of it at the time, but just avoided contact with them, as I believed they were bad people and I shouldn't associate with them. I was also cautious around the person I was told was a witch.
I have a number of stories I could tell about someone having a gift, and another person would comment about that gift, whether it was how smart the person was how beautiful their hair, skin, or face was, after the comment, something would happen that caused the person to lose the very thing the other person commented on, and the one who commented on that said gift, received the very thing they noticed and commented on, and the person that had the gift, they received what the other person had. Just like Satan received Adam's power and authority, which was a blessing of and from God, and Adam received the devil's curse.
As a short example, my wife's brother, many years ago, was a very smart young man in high School, until one of his friends mentioned how smart he was. Her brother was acing all the tests with no problem and his friend was struggling and was not very smart at all. Until she noticed the reversal. How his friend was starting to Ace the tests and her brother was failing in classes now. So what happened? How did her brother lose his intelligence, so to speak, and his friend gets so smart so quickly?
Was it witchcraft?

Was it witchcraft? I doubt it. It's far more likely that your brother-in-law started focusing his attention on other things, or encountered subjects that did not come easily to him. I experienced both in my schooling years. At the same time, his friend probably buckled down and realized the value of good grades and learning while it was still "free".

There's a principle known as Occam's Razor (the spelling varies), which basically says that the most likely explanation is the simplest. It appears to me that this principle is directly applicable in the situations you mentioned.

“The greatest trick the Devil ever pulled was convincing the world he didn’t exist”—Charles Baudelaire
I would not write off the OP's question so readily.

I didn't write it off.

So what happened? How did her brother lose his intelligence, so to speak, and his friend gets so smart so quickly? Was it witchcraft?

“The greatest trick the Devil ever pulled was convincing the world he didn’t exist”—Charles Baudelaire
I would not write off the OP's question so readily.

I think way too many people blame normal problems and struggles on demonic influence. Rain falls on the righteous and the unrighteous. It’s called life. Putting into practice lessons taught in the Bible can definitely help one to avoid snares but diseases, crime, and bad genetics are not demonic. They are all reasons we rejoice in a life to come.

I used to say, most sickness comes on a person due to their sins, but this past year has opened up a new area of understanding for me.
In my earlier years, I would hear a voice tell me certain people, actually it was always women, were witches. I didn't think anything of it at the time, but just avoided contact with them, as I believed they were bad people and I shouldn't associate with them. I was also cautious around the person I was told was a witch.

Was it witchcraft?

In the OP it goes back and forth from witches to Satan as if the terms are interchangeable. One Satan is real while the other witches are nothing more than the kindergarten class into the occult.

I see many of you are as I was in my teens and early twenties, a mediocre Christian, going about your life in your own little bubble, not knowing what's going on around you in the spirit world.
Many of you I would say are secular or carnally minded Christians.
I say that because many of the so-called, believers, look to the natural world and reasoning to explain away every ailment and situation.
I would like to tell you some of what I and my family have been going through for the past year.
After being married for 32 years to the same woman, wouldn't you think I would know just about everything there is to know about my wife? The fact is, I do.
My wife is a very special and precious no nonsense woman of prayer. She is almost always in prayer because she doesn't need to work. So while she is in prayer many times she will see things in the spirit world.
She also has very accurate dreams of what people are doing behind closed doors or in secret In other words, I see my wife as a very godly woman.
So what do you think that would do to me, her husband, when I watched her go from about 135 lbs down to 95 lbs, close to skin and bones, due to severe nausea, stomach pains, and diarrhea, in just a few short months after my daughter started dating a guy?
But it doesn't end there. All those who contacted my wife and I, also got the very same thing, and we never told them anything about what my wife was going through. My mother-in-law, who is wheelchair bound and 87 years of age, stop calling our house because she knew where it was coming from. My wife was having a very hard time so it would be even worse for her mother to go through the same thing, only being wheelchair or bed bound. And when I say severe it was very very severe. If you had diarrhea and you went to the bathroom seven times and a half an hour and do that all day and night, depriving her of sleep at night, and throwing up every time the smallest amount of anything went in your mouth including water, I would call that severe, wouldn't you?
But it didn't stop there to where it went to other people either.
Let's go to the part where my wife... Well, there's a disagreement between my son and I, where he thinks she died but I'm not so sure. Either way, we both were calling her spirit back into her body, as there was no one there while her eyes were wide open, after she collapsed on the floor.
She did recover from that incident but then it happened again, and again, and a fourth time. While each time was getting worse and worse. After the second time it wasn't my wife who came back but a spirit speaking through her. Only it was not a good spirit and it did not have nice things to say but it did spill its guts, so to speak. It told us its name, who sent it, what they were doing, why they were attacking my wife, which by the way, was because she was protecting my daughter spiritually from the very spirit speaking out of her, which called itself, soul snatcher. That's what its name was, and it was sent by a gathering or covin of witches. It told us that. Also told us it was her boyfriend who sent it to kill my wife, and then said, I was next. All the while we are casting this thing out of my wife, this thing is laughing at us through my wife. We did this three times. And the reason why they wanted to get rid of my wife first was because it was after my daughter's soul because she did something she should not have done, and my wife was standing in the way. They we're using mind control on our daughter.
The last time that thing took over my wife before she lost consciousness, it attacked her heart as well. Again, I don't know if she died or not, I'm inclined to think not, but either way, she was not there and something else was speaking through her and at one time, it attacked my daughter through my wife, claws and all. My son was there the whole time and he was the one who pulled my wife off from my daughter, because the thing was trying to kill her. By the way it wasn't just me casting the spirit out, but it was both my son and I.
We have never taken my wife to the hospital, she never wanted to go anyway and at the same time, we knew it was spiritual and that's what we went after instead of the natural remedies and treatments. She's doing much better now until my daughter gets home each night. Every time my daughter walks in the door, my wife starts getting pains in her tummy again, only now, she's doing much much better.
I only told you a very little of what has been going on with one person, which is by no means all that she has gone through or myself or my son. The only one that nothing has happened to for this entire year is my daughter.
We believe the guy is after her money and our wealth, because he's a miser and he lusts after money and things. Why do I say that, because he's trying to get her to marry him.
So I ask all the naysayers and carnally minded Christians, was all this and so much more done by witchcraft, rather voodoo, or is all of this just a coincidence, or happenstance, or is it because we're just religious fanatics and it's all in our heads?

I would say possibly it's demonic. There is some evidence in scripture that suggests Satan is capable of producing miracles:

Matthew 24:24 (NKJV)
24For false christs and false prophets will rise and show great signs and wonders to deceive, if possible, even the elect.

2 Thessalonians 2:9-10 (NKJV)
9The coming of the lawless one is according to the working of Satan, with all power, signs, and lying wonders, 10and with all unrighteous deception among those who perish, because they did not receive the love of the truth, that they might be saved.

Revelation 13:13-15 (NKJV)
13He performs great signs, so that he even makes fire come down from heaven on the earth in the sight of men. 14And he deceives those who dwell on the earth by those signs which he was granted to do in the sight of the beast, telling those who dwell on the earth to make an image to the beast who was wounded by the sword and lived. 15He was granted power to give breath to the image of the beast, that the image of the beast should both speak and cause as many as would not worship the image of the beast to be killed.

In my honest opinion, it's hard to rule out that those people just did something that made their skin and hair healthier like eat healthier. Or they were distracted by something that made them begin failing class because those kind of things happen, too.