I don't think a child would become gay because of his/her parents. If anything it would give the child a greater knowledge of acceptance within society.
Do you mean would the child be confused because their is 2 mums/dads? Well, I don't think this necessarily a problem, because if the child is young enough, then they will adapt. Children are good at accepting change.
I really don't think it matters about the nursing. But going by your theory, can't a gay male couple adopt a son, and a gay female couple adopt a daughter? There is help eberywhere nowadays though, like how to explain things to your children when you really don't know what to say. The parents will cope.
Yes. No "if"s, "but"s, or "maybe"s. There is really no reason why a gay couple shouldn't adopt a child, and if there is a reason, it shouldn't be related to the couple being gay.