about highschool: none of these kids really deeply care about you. they're just people thrown together you'll most likely never meet again. true friends will stand by you even if you hadn't told them the truth and they find out later.
there is no reason to tell people who don't care about you and your life what they would like to know out of sensationalist curiosity. Because really, what's the difference? a bio-guy is treated and regarded as a guy. in an ideal world, so is a trans guy. the only thing disclosing will ever do for you is making your life harder.
Saying "deceit is lying and lying is evil" is a very Christian view on the situation. The truth will make a lot of people see you as something you're not - how is that fair? going to school as a boy, most people won't even know you. Going to school as a transguy, everyone will know you - as the transguy. I adore your bravery for deciding to be openly trans at school and i hope it will all be for the best! for i sure as hell would have used the new school as the basis for a fresh start.
the excuses that murderers give for their hate crimes should not be a basis for your decisions. by that reasoning, no woman would be allowed to wear a mini skirt or lipstick. no little girl would be allowed to be outside on her own and there'd be no immigrants....well you get the picture.
your brother should support you on your difficult journey. at least he shouldn't be the one making it even harder.