If outright rejection is a real issue-caution might be a good idea. You don't want to lose the chance to have a great future. It might be good to start by testing the waters, and seeing how they feel about trans* stuff. I don't know for sure, but...that helped me a lot. No matter how they feel about trans people, this is going to be a really big deal for them; they might need some time to come around. My family wasn't accepting at first, but they didn't kick me out, and did come around eventually. Coming into this discussion with a clear head is important. Once you decide when (or, if) you want to have this conversation, you should write a list of talking points, things you want to cover, and try and stick to them. It's normal to be afraid about this, and using caution is important. But, if they really love you, they will come around sooner or later.