Ugh, your poor sister. Is there any way you could get custody of her without going through the whole filing and legal route? I mean, maybe she could just come spend the summer with you, or live with you "because of great schools nearby," or something? Maybe due to their health, you don't want them to have the "burden" and want to "help them" by taking her?  Just, maybe there's a way to get your sister out of that environment without having to go full Enemy, you know?  Given what you say about their opinions of your lifestyle, I guess it's a slim chance...but maybe it's worth considering. Even if she could just come for the summer it might help, and certainly my kids's schools are about to let out, so hers probably is, too.