Now for something personal

Alzheimers sucks. My father has it. It's a horrible disease. Slowly, each day, my father loses more of his mind. In the beginning, he knew he was losing his ability to remember. Now, he only acknowledges that "I can't talk anymore." When he speaks, he makes absolutely no sense. It is so sad.
He is literally losing his mind. Not in the sense that he is going "crazy," but in the sense that his ability to express coherent thoughts is slowly slipping away. He still recognizes my voice, but he doesn't really know who I am. Yet, at the end of our conversation, he will tell me that he misses me. He is in a home now and has been for the past five months so I know that he is safe, but it's still hard to watch someone you love die the way my father is dying.
My younger brother has it worse. He lives nearby and tries to visit him 3 or 4 days a week. My younger brother has a marijuana/alcohol addiction. I think seeing my father so often and dealing with the disease directly exacerbates his addiction. He was a pretty functional addict before, but now it's starting to affect others. The care manager has contacted me and said that she has seen him come visit my father drunk and them take him out on an excursion and she is concerned.
My sister lives nearby my father also and now she is on a self-righteous warpath to confront my brother about his addiction and give him consequences. She wants to organize an intervention. She wants to ban him from taking my father out of his "home." My brother just turned 30 and has been smoking/drinking since my mother died when he was 17. We have tried in the past to help my brother realize his problem, but nothing in recent years. He doesn't want to be helped. My sister, who loves tackling other people's problems, but cannot seem to solve her own, is all riled up. I don't know what to do.