It sounds as if it was a very hard decision, but that both Charlie and Sherpa are in better places for each of them now, and happy, loved kitties. I do not think you :failed" them at all. And adopting mama Celeste would not be any slight against them, as the situation with her are Kyubey seems to be working out good for both on them. Know you are in our prayers, and we hope you have a good birthday despite all the hard decisions!