The people that hate you are very immature and don't know how to respect the fact that a man is in a chorus, because men are very common in a chorus. Also don't blame the kids for hating, it's the parents fault for raising them like that. Defanetly tell your dad and have him contact the parents of those kids and have the other parents tell the kids to mature and respect people that are different.
I think you're being too critical. I doubt that your dads singing is that bad. Sorry couldn't resist. People don't hate people because their parents have a God given gift and they choose to use it. I think you're making a mountain out of a molehill. Sorry