Hi NTT,
Do you know of any Al-Anon groups in your area?
There's no easy solution to helping a loved one with alcoholism. There's often very little you can do except to not enable, that is, not to offer supports that allow the person to continue to drink while getting their physical and emotional needs still met by their family and friends. Exactly how and what that entails is something you may find people with experiences of their own are most knowledgeable of. Why I brought up Al-Anon; SR also has a forum devoted specifically for friends & family of alcoholics (below this one.)
The other crucial part, which is a big part of Al-Anon, is learning how to take care of yourselves in this situation. Much as you want to help your sister you and your family also have the right to your own lives and happiness. Having some independence from the problems revolving around your sister is something you deserve. Cold as that sounds, not being drawn into her addiction could actually be the best thing for her.