What would you do if it was your sister?

My sister who is 65 and her controlling bully husband raise their bi polar grandaughter who is 12, the father of the child is bi-polar they support him financially, but he does not live with them, the mother is not in the picture but she is bi polar also, The whole family is so dysfunctional its pathetic. My sister has had such a rough life and i feel so sorry for her, she is stressed to the limit. Her husband is a big bully and dictates the whole house.he has always been that way, she has always had to walk on eggshells and try and keep peace so he doesn't get all mad. He abuses my sister not physically but mentally by having it his way or no way. When i go visit my sister, which i do often i have to witness how unfair everyone is treated, her husband has always been an A hole, i have never confronted him about his behavior, never thought is was my place, of course my sister complains to me, which i really don't mind listening, but if i were to confront him and speak my mind he would probably make it miserable for me to see her, plus its such a toxic atmosphere to be around that by the time i leave im depressed. She lives 2 1/2 hours away so when i visit its for at least 2-3 days, i visit only for the sake of my sister, i want us to stay close. If it were your relative what would you do?