I am only having problems with alcohol as well. Yet I have a sibling (sorry still being a bit anonymous) living with me that has done meth for over 25 years.
The only real tip I can give, as i'm in a family that is dysfunctional some is this: "Think of yourself first". I know when you heard news about your mom that could really jar ya (would get to anyone), but if you need a safe distance then don't feel bad to use it. Find times when you can see your mom alone, and other family members aren't around to get on you if needed. Show your mom ways you care if you want to, without getting others involved. If your mom herself is being negative on you, and you don't want to get into it. You have to think about what could happen in chats with your mom and think of ways to defuse it. If you want to talk about it all and be open since your mom is in poor health, just triple check your ready for the good ole' (rough) "talk".
I'm new here as well. Hope my ideas help some. Just decided to post on your thread cause I have some family issues too.
B