I can very much relate to this. I worry a lot about my nephew who is almost 4 now. Both of his parents have handfuls of mental illnesses, plenty of anger and addiction issues between them. My sister has yet to really involve herself in his life and he's being raised by get ex bf (the father) and his parents. I'm not much a fan of them either.

I've talked to my t about this and how I wish so much I could rescue him and how I'm so worried for when he status getting older. T tells me that while maybe I can't rescue him to the extent I'd like, I can still be there for him. I can be a safe person to talk to and I can support him if he needs it.

I'm not sure how old you are, but you can do that as a sister too. You can't change their parents our their genetic predispositions, but you can be there for them. Listen and stay involved as they grow up. They might still encounter struggles but its a lot easier to get through then when you have someone on your side