Baalzebub is a lie. Satan is the father of lies. The Three Lies specifically which Satan told in the Garden are his unforgiveable sin and where all lies come from.
From reading the New Testament, we see that demons can inhabit people's bodies, drive them to harm themselves. They could talk to Jesus, all Him the Holy One of God. They could say they are legion for they are many. If you tell a lie, can that lie make decisions, wonder around, inhabit people, think, and do things? No it cannot.
In the Bible we see God is the Creator. I do not see where the Bible specifically says where God created the demons. He created the heavens by His word and the hosts thereof by the breath of His mouth. He created the earth. Do you have any evidence that Satan created demons? Demons may speaks lies, but they are not lies.
You also assert that Beelzebub is not real. Where does the scripture teach this? Elijah confronted the kings messengers with a message for the king, asking is there not a God in Israel that he would consult with Baalzebub the god of Ekron. Paul says that though there be that are called gods in heavens and on earth, to us there is but one God. He does not say that there is nothing behind paganism, but rather that he did not want them to sacrifice to idols lest they should have fellowship with demons.
On the one hand, you seem to hold to some materialist ideas about the spiritual realm. On the other hand, you are using this almost mystiscal-sounding esoteric wonky allegoristic approach to the Bible.
This is the demon's origins and also their being created by Satan forging the lies by breaking his spirit would be the blasphemy of the Holy Spirit.
Jesus was talking to human beings when He warned about blaspheming the Holy Spirit. The topic was not the fall of Satan. Mark even tells us the reason He gave the warning was because they had said that He had an unclean spirit. That was the reason, not all this three lies in the garden of Eden rational you present. Jesus indicated that He cast out demons by the Spirit of God, but they were saying He did it by an unclean spirit. So what were they saying about the Holy Spirit? What were they calling the Holy Spirit? In Matthew, we see that they were saying He cast out demons by Beelzebub, when the Spirit He was actually doing it by was the Holy Spirit. So what were they calling the Holy Spirit? This makes perfect sense because it doesn't require redefining 'blasphemy' into something else that does not mean 'blasphemy.' Also the wording there about no forgiveness for the one who speaks a word against the Spirit not being forgiven makes sense.