My parents' dislike for her is greater than my own. It's almost to the point where they can't stand her. I've told them multiple times that they should be totally honest with my brother about how they feel about his fiance. They don't want to, and probably won't, tell him anything like that. The reason for that is that they don't think it's gonna make anything change(something I agree with), and because they're afraid if they voice something like that to him, it might damage their relationship with their son, and they don't want to take that chance.
This is where I differ with them. First of all, their relationship with him is already deteriorating in some ways...when either of them goes to New York, where he lives(both of my parents have numerous reasons to travel to NYC on a fairly regular basis), they're lucky if they can get up into his apartment. And let's just say we have a hunch that that is because the fiance whines to my brother that she doesn't want us up there.
Also, when either of my parents are in NYC, you would think my brother would make time to see them, yet it seems like he is always just fitting them into his schedule....that doesn't have that much to do with HER though. Anyway, that's first. Second of all, the reason I think they should tell him now, is that I just think their dislike her is big enough that it is a matter of when, not if, it will come up. If I were them, I'd want control over when and where I told him, I wouldn't want to take the risk of it coming at the wrong time or wrong place. That's their call though.
My own dislike for the fiance is not quite as intense as my parents'(especially my mother's), but it's there. My biggest problem is actually not her directly, but really who my brother becomes when he's around her. It's like he becomes this kiss-ass, catering to her, too willing to give into her wants/needs/demands(nothing harmful that I know of, but that doesn't matter). Understand this, few people in this world know my brother better than me. Perhaps, outside of himself and our parents, no one does. And the guy kissing her ass all the time is not by brother.
The 'real' guy seems to come out less and less. This past summer, we took a family vacation to Cancun, just the four of us, she wasn't there. The parents shared a room, me and him shared the other room. And late at night we'd stay up late talking and watching sitcom re-reuns on TV and chit-chatting and what-not...that was one of the few times in recent years that my brother has shown his real self.
Now, despite the fact that I tell my parents to come clean with him, I wouldn't do it myself. The reason for that being that any truth-telling I do with him concerning this will inevitably lead to my parents getting involved, and if they don't want to do that kind of truth-telling, then I'm not getting them into something they don't want. And they're right about one thing; telling him won't make him change his plans to marry her. So my mouth is shut.
I can live with it, I guess. But the one thing I think about a lot is, what if he asks me to be his best man? I have no idea if that will happen or not, he may well ask one of his friends, who knows. The point is, if he DOES ask me, then what? I would hate to say no to something like that, but I also really detest the idea of standing behind him on his wedding day with at least a partially fake smile on my face pretending I'm happy about what he's doing. Don't get me wrong, I'll be at the wedding either way and I'll probably be doing some smiling, but being at the wedding and being the best man are two completely different things, and I really don't know if I want to have to fake my through something that shouldn't have to be faked.
My brother could find such a better match for himself, instead of her. He could be making the biggest mistake of his life. I honestly can't see a marriage between the two of them lasting very long.