I definitely would not go to the wedding, and I'd ignore all of them, including my mother. I can't believe anyone would go for a bachelorette weekend and think it's okay to just ignore half the guestlist.
The only thing in this scenario that I think OP did wrong was the wording of her text. I do think the text was bad, as OP says, and while OP says she's confused about the whole mess, I have to say that if someone sent me an email like that, I wouldn't want her there for my wedding,either. I wouldn't want someone there who spoke to me like that. I think the bride's ticked off about the text, understandably so, and she's only extending the invitation because she also cares about the brother having his family there. I'm not taking the bride's side, because I do think she was way out of line, but I can see her perspective.
Maybe she acted the way she did because she was so stressed about wedding plans. I don't know. Regardless, her behavior was completely inappropriate.
OP, I think I would apologize, sincerely, for the language used in the text (you've said yourself it was bad). That apology would be couched, however, with reiterating (calmly, without profanity) why I was so upset in the first place. It's just plain bad manners to behave that way toward the individuals who travelled a long way to spend time with you, especially people who spent a lot of time and money to try to make the weekend perfect for you. I'd also tell her what I thought of her firing DD from the wedding . . . completely childish behavior toward someone who did nothing to deserve it.
Even if FSIL accepted the apology for the tone of the message, I wouldn't go to the wedding, and my brother and mother would both be getting the cold shoulder from me. I could understand why the brother would take the bride's side, but my mother . . . nope, I'd be ticked, and she would know it.
I think staying away is best to avoid any additional drama, and also because it would be ridiculously uncomfortable to be there where it's clear you're not really wanted. If you don't choose to completely ignore him, I like the idea someone had of sending your brother a card wishing him well and offering your love and support.
As for OP's DD, I love E-Mom's idea of showing up in the MOH gown. Priceless, the kind of thing I wish I had the nerve to do.
OP, I'm sorry you're in this position. I've been through similar family fighting, and it truly is heartbreaking. I hope you will all be able to mend this in time.
