Hello everyone. I haven't read the whole thread yet (I will), but there are so many resonances with my childhood/adolescence that I had to post.
This is a long post - sorry x
to all of you - my heart breaks with each of these stories, they feel so familiar and painful to me.
My dad remarried when I was about 10. My SM left her very small children (4 and 6) in their home country (because their DF wouldn't allow them to leave) and proceeded to take all her sadness, anger and guilt out on me and my DB. The atmosphere when we visited was hideous. She regularly ignored us. And if she wasn't ignoring us she was attacking us. There were no photos of us in the house - dozens of her kids. Her kids had rooms of their own, beautifully decorated with toys etc, though they were only there a few weeks a year. My DB and I slept in whichever spare room had least junk in it.
At some point, she told my dad that if she couldn't see her kids, he couldn't see his. And he basically gave in to her

For years I hardly saw my dad. When I did, he constantly cancelled or rearranged at the last minute. And if we did eventually make it their house, it was very very clear we weren't welcome.
My dad and SM used to have the most hideous, volatile rows (which I largely understood to be my fault). Then one day, when I was late teens, I saw my SM punch my dad. I had to stay with them all weekend, my DB wasn't even with me. I'm crying typing this now and it must have been 25 years ago.
In my late 20s/30s, I didn't see my dad for about 10 years. He'd occasionally ring, to tell me about a row he'd had with my SM, or ask to borrow money. I finally saw him again in a psychiatric hospital - he'd been sectioned after trying to kill himself - she apparently tried to persuade him to do so, to clear their debts

They're now divorced, my dad is very vulnerable and ill (we have some contact these days) and my exSM continues to bully him.
I am extremely angry with both of them. This stuff has been a huge part of my ongoing therapy.