Quint ROFL!
No, I am not the future SIL; I got the impression the SIL has no kids, so doesn't post on MN.
I was just trained well by mum NOT to get involved with the relationship issues of other family members.
There are loads of problems like this on MN all the time. I think that if a man has grown up with sisters and a mum who say 'do this', do that, then he will end up marrying a woman who also says 'do this, do that.' Then you get a man like the OP's brother who is passing messages between future wife and sister. Why doesn't he just say to his sister, 'this is my wedding, my day, and this is what I want?' Because he appears to have no mind of his own! He just passes messages between 2 fighting women who are going to have a row.
I make no judgement on my SIL, her wedding, children, house, work patters etc, because it is NONE OF MY BUSINESS. My brother chose her, and its his life, and he is an adult. I just wish families would try to get along.
I really do think it is mean to call your future SIL a bitch and question her future husband on the sense of his marriage.