^Yup... denial. Complete and utter denial. They've written their own life script for you, and as such they are trying to find any excuse that they can for why the things that you say aren't true, and why you are still the person that they think you should be in their own eyes, and they're fighting back against it, and refusing to believe it, because they've always seen you a certain way and just can't imagine changing that.
It happens, dude. And unfortunately, it's not always easy to change. I'm having the same denial issues with my dad right now. He's constantly trying to explain it away, says things like "well, that doesn't mean anything" and "come on, you're joking, right?" when I try to explain to him why I've always felt transsexual.
In your case, with how strongly they are pushing back, you really are going to need to get out of the house as soon as you can do so. Because as long as you're still living there, it sounds like they're still going to think that you're just being bratty and rebellious. I really do believe that their tone will change if you move out, and are living on your own, and yet you still keep pursuing transsexualism. It's easy to belittle your kids and fight with them and fail to sympathize with them when they're still living in the same house, but when things still persist even after moving out and starting your own life, the tone really does change.