Well,the cats out of the bag. I recommend you come clean. The whole truth. It will be weird but it will be behind you. I think you should tell your brother first,alone. It will do two things for you: 1) give you practice with someone less judgmental than your parents and 2) experience the reaction from him which I will bet is far more low key than you expect.
You will be embarrassed but then it's done. With him on your side, you come out to the parents. Be ready for the "are you gay" and "do you want to be a woman" questions. Have material ready for them, like this site or better yet, TriEss or other independent organizations.
Lying is not an option. No story will,make sense now. Odd as this will be, it will be liberating. Good luck.