I wonder if you could ask your sister to let you take the children to an al-anon for kids meetings? They are surely bearing the brunt of all of this.
I am so sorry for your pain. I had almost an exact situation growing up. My sister began drinking as well, with two children of her own having to live with her borderline personality disorder and drinking. I tried to reach the children with some literature, and my sister just became indignant, and the kids were out of my reach from then on. They were protective of their momma, even tho they had voiced their unhappiness with her behavior. She eventually stopped her drinking, but the kids were forever scarred.
My sister did not admit any wrongdoing, or problem with alcohol.
If your sister listens to you, perhaps it would be good to tell her that if she does not care about herself, she might consider her children, before childrens protective services have to be involved?
This is taking away their childhood, and setting them up for future pain and dysfunction.
Perhaps you could give her the information on AA meetings nearby, and for al-anon meetings for the children.
I wish you and all the family safety and that your sister hits her bottom without taking the children with her-tho that is pretty much how it usually happens.
Maybe you can talk to the children? I would imagine they need someone to help them, desperately. it is very frightening to hear your parents fighting and hitting. children fear their parents dying, and leaving them alone. I feel so sorry for them-their lives must be awful, and they must feel so alone. I remember feeling that shame, and it continues to be a fight for me to feel "as good as", you know?
prayers for your family,
chicory