You can't do much. If your sister does not choose to get into recovery, she's not going to begin recovery. You cannot force someone into a recovery program and it wouldn't work even if you could unless they wanted it to work.
It sounds to me as if you and your parents need to get to AlAnon, educate yourselves about alcoholism and what it is doing to all of you. Enabling her alcoholism doesn't help her. It does hurt all of you.
If the children were not safe, you could consider trying to get custody. It doesn't sound as if things are that severe though and I doubt the courts would go for that.