Hi, DorotheaSofia.
I was child number eight out of nine, and my own parents divorced when I was twelve years old. Like you and your siblings, my siblings and I witnessed many horrible interactions between our parents, but, truth be told, we weren't the cause of any of them. One of my brothers died when he was only six years old (before I was born), so eight of us (one has since died, and both of my parents are now dead too) continued on after our parents divorced, and five of us basically came out unscathed, but three did not. In fact, two of the three still seek counseling today, and my parents' divorce was about forty-seven years ago.
Although I came out fine from the get-go, I actually gained a much better understanding of both of my parents long after they divorced which helped me even further. My mother actually wrote and published a book about her life, and I had never read it, even though I had a copy of it for years. After I eventually read just the first chapter many years ago (that's all that I needed to read), I gained an even better understanding of how we (my siblings and I) were never a part of the problem. In other words, my mother carried some horrific events from her own childhood into her own adult life and marriage, and it was basically "deja vu" or history repeating itself.
Near the end of his life, my father typed out his memoirs (only about 30 pages or so), and gave all of us (me and my siblings) a copy of the same. As with my mother, it was basically "deja vu" or history repeating itself in that he had a horrific childhood as well that he carried with him straight into adulthood and marriage.
My point is that all of these things which greatly affected their adult lives and their marriage transpired before any of us (me and my siblings) were ever born and before they even got married to one another.
It's possible that the same principle applies to your own parents, and that what you're witnessing between them is just a reliving of their own pasts as well, before any of you were even born, so try not to blame yourselves for anything that is currently transpiring.
In my own case, I was married for eighteen years (we were pretty much separated for the last three), and my ex and I had three children together. Currently, they are 18 (daughter), 15 (daughter) & 13 (son), and they've definitely been negatively affected by things they witnessed when my ex and I were still together, YET they've not only gotten better since we divorced (my ex cheated on me multiple times and then divorced me), but they're also happy that we're no longer together. They presently live with their mom, only about 10 minutes away from me, and i see them all the time, including earlier today.
At my end, I honestly did everything imaginable to stay together with my ex for at least two reasons:
1. I had entered into a covenant of marriage before God, and I didn't want to break it.
2. I wanted my children to grow up in a stable environment, and I would have died a million deaths if I could have guaranteed the same.
I truly was willing to sacrifice my own life for theirs, so this might be what one of your parents feels as well.
Whatever the case may be in your family, you cannot blame yourselves for any of this, nor can you define your own self-worth by any of this. Their failed marriage isn't a reflection upon you, but rather upon them.
As far as encouragement for you and your siblings is concerned, I would encourage you to try to see yourselves as God truly sees you.
I don't know if you've ever sold or bought anything online (ebay, Amazon, etc.) or maybe even at a garage sale, but you can determine how valuable something is by the price that somebody is willing to pay for it.
In the case of you and your siblings, the price that God is willing to pay for you is the sacrifice of his Son, Jesus Christ.
THIS is your true worth, and NOT anything that is going on presently between your parents.
In the midst of your ordeal, please try to look up towards God through Christ, and he will provide all of you with the grace necessary to not only get through all of this, but also with the grace necessary to ensure that history doesn't repeat itself in your own lives later on.
You can have stable lives yourselves, even if you start in an unstable environment.
Hopefully, this will be of some help to you and your siblings.