Hi, Dominique. Well done for stating your case to your parents.
Mine were quite a bit like yours. Dad was violent, hated everybody, and made us all feel like shit including my mum. Now I am twice your age, I hold my mother responsible, also, for the problems that my sibs & I grew up with. But this is an issue for you later, maybe when your children are older ...
She wants you all to "make friends" because this will repair her fantasy of a happy, united family. She doesn't see it, of course, but she's asking you to deny the truth of your life - so that she can carry on hiding her own pain from herself. Obviously, that's not the greatest idea.
But if you, like me, see no merit in making your mother's life worse than its - what to do? You can't force her to see things the way they were, that would be a kind of mental torture for her. People reconcile with the truth at their own pace (or not at all); I've reached a half-understanding with my mum, who is 80 now. It cost her immense pain to get even half-way; I'm grateful for her effort but I've always known there was little chance of reaching full understanding with her. It would be intolerable for her, quite literally.
When I was your age, I called my dad into the dining room and gave him a very short speech about how I despised his violence, lack of support and insulting behaviour towards me and the rest of my family. I asked my mother to attend - she listened, but she hid in the kitchen because she was so afraid of his reaction! Dad was OK with it, though. I was really quite moderate - just factual. I said I spoke only for myself, not for the others, and that I wanted nothing to do with him for a minimum of two years, while I began to free myself of his influence. I asked him to respect my separation. He said yes.
For the next two years, I would phone home; if he picked up, I just said "hello, it's Grace, let me speak to mum/brother/sister". He did, like a lamb. When I visited, I asked for dad to be absent. He was.
Domineering fathers rule their households, it's difficult for any member of their "retinue" to challenge their authority. Their wives are their slaves. But you can challenge. Just don't ask his wife to support you; she has more or less lost her own identity - it's cruel to her, to ask for rebellion. Challenge him, as clearly and directly as you can (in person, if you can arrange it). Set out your terms. Don't set terms for his wife, it's hard enough for her already.
I hope it works as well, for you, as it did for me! Good luck