Adopting my sister-in-laws baby

My sister was diagnosed with MS after my nephew was born in 1991. She then had a daughter and was in aggressive treatment for her nerve damage and the stripping of her myelin.Fast forward 15 years and my sister is getting progressively worse. She gets extremely angry because her body is deteriorating and she is a brave, determined person that craves a life free of this disease ravaging her life. Her husband turns to another woman and destroys any remaining self-esteem she has left. She turns to (legal) drugs and alcohol to deal with the heartbreak and humiliation.On a few occasions, she lashes out at her, now, teenaged children that have their own destruction going on. This gets blown out of proportion in the eyes of the police, the custody judges, even in our (her family’s) mind's eye.She is falsely arrested and charged with bogus, blindly prejudiced charges of harming her children. She’s about to die from her disease but no one can see the forest for the trees.Her children are unable/unwilling to stay with her at this stage. So my mother and I step in and get guardianship of the children. Now, I’ve just had my own two children and because my mother has a previous domestic violence charge my father and I get the documents signed and pushed through. Primarily because the state is stepping in and making recommendations to place the children into foster care. Not on my dead body!My sister's disease and alcoholism strip her of her personality like a thief in the night. They leave a shell of a person unrecognizable to anyone that knows my sister but far be it for anyone to add insult to injury. She died alone in her house. Her heart gave out when she fell out of bed and couldn’t regain consciousness.I ended up with legal custody because the children’s father stood up in court and claimed he wanted his parental rights terminated. Against everyone’s urging, he made up his own messed up mind and left. This caused my mother to have a heart attack and die.Last I heard, he was remarried and a “wake and baker”. So high on weed that he has the state record of a living person on cannabis.The two kids ended up hooked on heroin. My niece is completely out of contact with everyone. Living with some guy out of town. My nephew took my sister's house when she died and is on daily doses of methadone. He has a job.If I had it to do over, I would have…done the same thing. Some things are out of our control. I made the best decisions I could have given the options.That doesn’t make any of it okay.Think very hard before getting involved in other people’s lives.