I've actually been out to my brother for a few months, now, but last night I had a lovely talk with him.
He's been having kind of a hard time adjusting. Understandable, seeing as I've been his sister for as long as he can remember-- he's not accustomed to seeing me as anything else. However, last night he informed me that he understands this is my identity and that it's here to stay, and he's making an effort to adjust. He also came up with a fantastic compromise-- for the time being, he's going to keep calling me by female pronouns in real life (partially because that's what he's used to, and it's harder to adjust verbally than in writing, and partially because our parents would eat him alive if he did otherwise) but use male pronouns for me online.
Of course, I gave him a high five and informed him that he wins at life. |D
...now the big challenge will be my mom. My brother gave me some updates, last night, on the things she's been saying behind my back. Apparently, she thinks it's just a phase and I've been being corrupted by my friends. Somehow I'm not surprised-- that was the impression I'd already been getting from her, but now it's confirmed. Wish me luck? I still haven't indicated to her that I plan on transitioning, and I have a feeling she won't take that news well at all.