If you don't like the girl, then WHY on earth would you want to be a part of her bridal party?
I mean, if you have ever been in a bridal party, you know how it is ALL about the bride. There would be showers where you would have to ooh and aah over slotted spoons, etc. You might have to gush over how pretty she looks when in reality you HATE the gaudy number she chose to wear.
I don't think you actually want to be in the bridal party. Perhaps, it is just the thought of being left out.
Everyone is correct in saying that your brother should speak for himself. If he isn't, then he's sending out a loud message of either being completely whipped or of being passively aggressive in letting her take the rap for things he had no desire to do (such as visiting, etc.)
Wrigley is right. She WILL call the shots on the grandkids, where holidays are spent, etc. So, you better just grit your teeth and bear her for as long as she is around. These days, marriages don't last that long