We all know the story of Hazrat Musa. He never drank the milk of any other mother who was kafir. He only drank the milk of his own mother who was not kafir. Because Allah would not let his prophet to be fed on the hands of a kafir. Then how can Abu Talib be kafir?
Fanatic
While you have explained how Musa p.b.u.h never drank milk of a kafir mother can you also explain which place was Musa p.u.b. was brought up. I mean whose house it was. As far as I can remember it was the Pharoah who claimed he was the God Almighty. It is just a way of Allah to show sometimes he can use kaafirs to help unconciously this very deen. If Musa p.b.u.h. can be brought up under pharoah I don't see why Mohammad p.b.u.h can't under Abu Talib.