A little background...
My wife and I are going to try to take custody of her little brother. His mother has repeatedly proven herself unfit to be a mother, at least until she gets sober, and he needs to get out of that situation... that's the bottom line, regardless of who he goes to. It makes sense for us to take him in... we're financially capable, he knows us and is comfortable with us, my wife is already in the will as his guardian should anything happen to their mom, and he's coming to stay with us over the summer anyway (he's in CO, we're in NC).
The people close to the situation (wife's older sister and grandparents) all support it, but getting his mother to go along is going to be difficult. My wife gently and indirectly brought up the idea to her mom of him moving out here with us for a while and she flipped out.

Where do we start? Nobody we know has any experience in this kind of a thing and we aren't really sure where or what the first step is.