If it was me, I wouldn't go. If your brother doesn't respect or care for you enough to call you by what and who you are, then he doesn't deserve the honor of having you at his wedding. Weddings guests are those that you love for who they are. And that's a 2 way street. If afterward someone calls you screaming asking why you weren't there, tell them the truth. You weren't invited.
A similar situation happened to me this past xmas. Me, my wife and her parents were going on a cruise. Her parents told us that Jennifer wasn't welcome. But (male name) was welcome to come. I told them if I couldn't be me, I wasn't going. And since I wouldn't be going, my wife said she wouldn't go either. They were pissed about that since they had bought the flights and tickets, which just happened to be non refundable. So they backed off, but were still derogatory the whole trip. It got so bad, that I quit eating with them, and went up to the deck where the grill was and just ate hamburgers and hot dogs the rest of the trip. And if there was a show we were all going to, I wouldn't sit near them either.
That was the third cruise I've been on. And that one was so bad I swore to everything in existence (tangible or intangible) that I would never go on a cruise again. The wife asked if she wanted to go on one, and I told her she would be going alone. And I meant every single word of that.
I guess what I'm saying is pick your battles. You're in a war, the same as all of us, but just because they are on the battle field with their weapons raised doesn't mean you have to engage them on their grounds. But be ready for their advance.
