She occasionally sees him when she visits her grandmother. OP has met his fiancee a couple of times and said she is fine but that they have very different lives and priorities.
However, OP acknowledges that she is great for her brother and is happy for them. She said that her brother’s fiancee is very high maintenance and is obsessed with having her “dream wedding” and being a princess.
What OP said made her SIL cry, and her brother called her angry, saying if OP didn’t apologize, she would not be invited to the wedding. OP said she is seriously considering not apologizing and not making the trip.
She sounds like a handful. And then wants you to do the work anyway. Don’t apologize unless she apologizes for treated you poorly because your pregnant.