This is just more of the same from him.
He doesn't care a whit for any of his children.
He is highly abusive.
Honestly I would really not go there.
Of course she wants you to stay with him but she doesn't know just how abusive he is.
Her mother left.
Your loyalty is to your children and getting them away from this dynamic.
I would keep reminding yourself of not wanting your children to end up in abusive relationships.
She is an adult and when this is over I do not think you need to be protecting him.
I would spell out to her EXACTLY how you have been treated.
In the interim I think it is perfectly reasonable to tell her you "understand that this is hard for her, BUT, YOU have been desperately unhappy for YEARS, at his awful treatment of you, and that what is actually best for the boys is that they are no longer growing up witnessing a highly abusive relationship".
She is an adult, she no longer needs protecting from the truth.
This is so hard and you are so brave.
Leaving an abuser is never easy because he wants you there to be his skuvvy and emotional punching bag.
"He had years to treat you with a bit of decency and kindness, he chose NOT to.
YOU are NOT responsible for the consequences of HIS behaviour."
Please keep reminding yourself of this.
And keep posting as it is a great way for you to put order to your thoughts, express your frustrations and is a great diary of your progress, of which you have made great leaps.
This is hard but you have a great life ahead of you.