You will successfully complete your transition Tammy, I have no doubt in my mind. I'm puzzelled why you have such a precise countdown to it though?
You probably can't ever know how someone will react. I am scared stiff of telling my dad because I'm frightened I might loose him. I think it will soon be out of my hands as my body changes are getting to the point where delaying things much beyond this winter would not be feasible.
I understand why telling your brother is so scary. He is your last real family connection and without him you will feel alone. But I see you on here Tammy, you make me laugh my butt off most days when I check out your blog. You will easily find friends and maybe a partner who loves you once you emerge as your true self. Tht sid it would be far better to have your brother in your corner too.
This visit, I would just make it a memorable one, do everything you want to do and everything he wants to do. Let him know how much he means to you. Then before he comes on the next visit, that will be the time to tell him, so if he reacts badly, you still have this upcoming wonderful memory of him.