I just read this thread for the first time today. Are you adopting a little boy that has two sisters elsewhere? I can tell you a story about just such a thing. A child was placed in foster care. After 2 years the child went up for adoption. The foster family considered adopting the child but followed the advice of all the "experts" instead. The advice was to put the child with two other siblings. None of them(the siblings) knew each other. After 3 years the child still wants to be with her "family" (foster family) and she has no connection with the amom at all. It has caused a lot of grief in two families. In other words I think you did the right thing by leaving your boy where he is.
M