This is very painful, I know. Despite your many accomplishments and the fact that you are doing your best to be a good son, you are being judged and ridiculed by the people you love most.
Here’s the thing: People usually react to differences in others because they are scared. Often they have been raised to believe that other races and sexual orientations are bad, immoral, and dangerous. It’s really, really hard to get beyond that early training. It’s really, really hard for parents to see their children going down roads that they themselves were taught to believe were harmful and dangerous. It’s especially hard when other people in their community share those negative beliefs. (I’m guessing that may be the case.)
Nonetheless, your parents also raised kids – you and your siblings – who can love people for who they are and who don’t reject people because of differences. They must be doing something very right! You’ve all also had the advantage of growing up in a time when the media and those around you are accepting diversity. You are part of this generation. Your parents are part of the older, less accepting one. This is bound to create tension in families.
All this philosophy may be interesting but I know it doesn’t really help fix the pain of your current situation. For that, you need more information and support. I suggest you check out PFLAG (Parents, Families and Friends of Lesbians and Gays) of to see what is offered locally. There may be family counselors available who specialize in helping family members like yours get to a new place with each other.
I wish you well.