My dad was emotionally and mentally abusive, sometimes physically abusive but mostly the cruelty. It was directed at all of us, my mum included, and she didn't leave him until we were all over 18.
His temper was horrific and even though it meant a worse reaction if we got caught we would deliberately hide things from him and cover up for one another to avoid getting into trouble, mum would help in this collision although I didn't realise it at the time. She would let us do things, go places, give us stuff and say "don't tell your dad". If one of us misbehaved she would tell us off in a totally normal way, she never ever hit us, and she would tell us all not to tell our dad we'd gotten told off or else he would give us one of his telling offs. If he started on us she would jump in and argue back with him, sending us upstairs or out to play first. I used to wonder why she did that and now I know it's so that he would be angry with her instead of us, it was part of how she protected us.
I've spoken to her about why she stayed and it all comes down to the reasons @katalavenete posted on page one of the thread.
She was scared.
He told her that if she tried to leave he would take us, legally if he could and illegally if he couldn't. He had dual citizenship and said he'd take us abroad so she wouldn't ever get us back. When he was being financially abusive she once shoplifted a coat and some shoes which she returned next day for a cash refund. She knew it was wrong but she needed money. He told her he would go to the police and she would be jailed, it would also result in her losing custody of us. He told her he would kill her, kill us, and then kill himself. He would show her newspaper articles and magazine stories where men had done that exact thing. He took her on trips where he'd show her exactly where he would bury our bodies if he ever had to kill us. He told her that women's refuges were full of drug addicts and people who would steal your stuff. That they would rehouse her miles away from her family and friends. That she would have no money other than benefits and there would be no maintenance from him. That no matter where we went he would find us because he would never stop looking so we would spend our lives looking over our shoulders.
She stayed to protect us because he had her afraid that leaving would make things worse. At least if she was there then she could run interference and get in between him and us.
There was a lot she didn't know too. The times when she wasn't there and he would start on us for the usual things - looked at him in an insolent way, being too loud, being suspiciously quiet, back answering, etc. - we rarely told her about them afterwards because he had us scared too. He would tell us that mum had told him to speak to us about our behaviour so then what was the point of going to her about it after if she was the one who ordered it? Or he would tell us that if we told her then she would realise how unlikeable we were, how unloveable, because only unlikeable unloveable children get told off like that and we didn't want her to learn the truth about us or else she would leave us. He said that he would ring the children's home to come and take us away because they would happier without us and if we upset our mum by telling tales about our "chats" then he would remove the source of that upset (us). He would do drills where he would drag us out of bed, make us pack a bag each, and then make us sit on the doorstep to wait for the man from the children's home. We had to say our goodbyes to one another because we'd be split up on arrival. After a while he would let us back in and back to bed but again with the warnings not to tell mum.
When she eventually found all of this out she was horrified and said if she had known then she would have risked leaving with us instead of waiting until we were 18. She waited until we were 18 so we were free of him and she only had to get herself out, she thought it was less risky. Even then he tried to follow through on all those threats he'd made over the years and attempted to kill her and two of us, made very specific threats that resulted in all of us having police markers on our homes and safety devices fitted, it was awful enough as adults and I'm glad now that she didn't try it when we were children because I don't think we would have come out of it alive.
I'd recommend therapy, OP. Lots and lots of therapy. It helps.