My first thought is that you should send your father a letter with some current pictures in it explaining your dilemma. Has he seen you dressed properly yet? Maybe he will be able to realize that you are not the son he thought he had anymore.
Of course, he might take a look at the picture and ask you not to show up at all.
Maybe a letter without the picture explaining your issue might be better. Or, you can just show up in men's clothes wearing a bra for support and letting him see how obviously female you still look. Tell him the problems that come without support, your mom may just back you up on that.
Or, finally, you can say to them that you are who you are and what they wish for is simply not possible anymore. Plus if you are doing your RLE for GRS, wouldn't reverting back again make it invalid?
It's a tough choice, Robbie, and I don't envy you. Good luck with whatever you decide.
hugs & smiles
helen