Great relationship with SIL but SIL hates my mum

Then yes I’d expect them to start pulling away from you while your children continue to spend time with your mother.

If they believe she’s too bad to be near their children they will believe she’s too bad to be near yours, they will wonder why you’d put your children in harms way be being near her and start to not trust you with their children’s best interests or safety because you don’t believe your mum is that bad and excuse her behaviour.

Now you've said the abuse is so bad SIL feels her MIL is not prioritising the safety of her children it changes everything.

I know how hard it is to leave someone abusive. I also know allowing my children to be unsafe, and myself, is a cut off point for sympathy.

As long as you don’t become a flying monkey, try and excuse her behaviour or tbh talk about either parent in front of their children you should be fine.

however if you have children? Or when you do if you don’t currently. I’d expect them to pull away if you are still in contact with your mother and father because otherwise they would be complicit in watching you let abusive people be near your children posted too soon, and then your children would be near theirs spreading whatever nanny and grandad are saying to them.

This will be 100% about protecting the children from abusive situations.

If you and your brother living in a abusive house where threats of murder where made and loud arguments went on for hours with violence are called spoilt and entitled by your mother because you had it better than her, is not going to be able to be an appropriate grandparent.

Until she changes her mindset on that alone she completely shouldn’t be near children. Because it means she sees it as normal to behave like that in front of children.

You are coddling your mum you need to firmly tell her that she is correctly facing the repercussions of her poor choices and that you won't discuss it with her again.
Also you need to stop allowing her to manipulate you into being her flying monkey with your db and sil.
I'm sorry to say this @pnakolada but you are so far into the FOG that you can't see quite how bad a picture of your mum that you're painting, she's a manipulative emotionally abusive woman. She is manipulating you into lecturing and attempting to guilt trip your db and sil into seeing her that really abusive towards you, your db and your sil.
If you are unable or unwilling to end the cycle of abuse that you've now become a complicit part of you need to expect your db and sil to go NC with you aswell, because your choices and actions have consequences too

Surely then you must understand why your brother and SIL want to cut your mum out of their lives? She calls her children, who had an abusive childhood, spoilt and entitled! She defends your abusive father! She is denying your realty. It's a bit like the narcissist's prayer, i.e. it didn't happen, or if it did it wasn't that bad, or if it did, you deserved it. She really isn't a safe person to be around her grandchildren.

You sound like an awful human, I feel sorry for your friends.

I grew up with an aggressive violent father and an enabling mother too. I do understand now she was in a difficult situation as there wasn't as much help back then. But I don't forgive her for the damage her staying has done to me and my sibling. I am still very angry with her and if she had minimised the abuse then I would have also cut her off. My mum's dad was also very abusive.

By staying with him and minimising what has happened she is presenting a very dangerous message to your brother and SIL's children. I would make the same decision.

At the end of the day, being a victim only goes so far. You and your brother were vulnerable children and she should have protected you. At the very least she should stop telling you that you had a good childhood.

If your dad has threatened to kill her if she ever leaves and he has been violent in the past then she is probably terrified of leaving.

Staying at yours or your sil's is unlikely to stop him.

She is making a perfectly rational choice. Many men who threaten this do carry it out and the police rarely stop them.

Your SIL is entirely correct in keeping herself and her kids away from this shit show.

Your dad is clearly a very dangerous man.

I wonder if she has started putting down the grandchildren the same way she does you and your brother (even just once) and that’s was a flag that both your brother and sil said no way is this happening to them?

I can guarantee you you don’t have all the facts of every incident that has happened to your brother/SIL as there will be small things never brought up too.

I don’t think they are cruel. I think they are putting their children first.

Your mum is doing the classic bullying you two, saying she is better at stuff etc that kid bullies do when they are put down. To have that power when they are the bottom of the pile, to feel that control for once.

People have an amazing low bar on the shit they tolerate from their parents - there is a need to be loved and accepted by them.

The SIL seems to be the only one that can see how messed up things and that’s the benefit of being an outsider.

I mean this really kindly, but I think the real reason you don’t pull your SIL up on this is that deep down you kind of agree with her.

you clearly love your mum loads and are a lovely daughter, but even so I can see the resentment coming through your posts. You know it’s a messed up situation.

I think you are probably actually doing exactly the right thing in treading a middle path at the moment. Let SIL do what she needs to do. Explain to your mum kindly why she is doing it. Encourage your mum and maybe seek support for her to leave your father.

You are all adults and it's none of her sodding business how your family has worked both before she arrived and since, unless you father is abusive to her.
Yet you would rather maintain a friendship with her?

Wow. You'd rather know your mother was treated badly, yet you won't open your mouth to stop it because you don't want to fall out with the perpetrator of this treatment?
Sorry, but that's appalling.

And you enable this SIL behaviour by refusing to criticise SIL as you are scared of SIL falling out with you

🙄

Why are you letting yourself be in the middle of this? Tell them that you will be longer listen to them slagging each other off.

This whole horrible situation is being caused by a horrible abusive man and yet you are asking about how to change the behaviour of your mother and your sister in law. The irony of expecting all the women (including yourself) to adapt and adjust because of the actions of one awful man.

You are so deep in this that you are complicit with your mother to excuse the behaviour of your father and just accept it like she does. You’ve been conditioned do to this but your SIL can see it from the outside and doesn’t want to just tolerate him for the sake of keeping the peace. If she does then he is basically controlling you all and has free rein over you all - and all the grandchildren …

it isn’t your mother, or your sister in law or you. It’s him. He is the problem.

So, your mum doesn't even acknowledge your father's abuse and thinks that her marriage and your childhoods were very good?

I can totally see why your brother and SIL don't want her around their children. She is denying that your father was abusive. That would be unacceptable for most people.