<human>: Can you summarize the given text in a few sentences?

My brother is marrying his long-term girlfriend (they have been together for 10 years). They are very close, and for the past eight years they have shared house, car, dog and friends. It is very difficult for me (and them) to picture their lives apart at this point.

Knowing both of them pretty well, I see a problem in that they strongly disagree on the subject of having children. My brother is adamantly opposed to the point of actually believing that everyone who has children regret it (and lie to themselves and others about the "special magic bond of happiness" that appears between parent and child), while his fiancee appears to think children are the only path to happiness in life. Obviously both expect the other person to change their mind as soon as they are married, and just as obviously (to me), they are not going to. They have talked about it, and always end up agreeing to disagree ... Which I think is just agreeing to continue trying to convince the other that having a child / not having a child is the obvious best choice for both of them.

Now, I don't want to be the person to potentially break up a marriage before it happens by pointing out this fact to them. I know I don't have privileged access to the "truth" of their relationship, being an outsider, and that I shouldn't make assumptions on their behalf. But I also feel I have a bit of an obligation, particularly towards my brother, to help him reflect on this issue a bit more thoroughly.

I think the main problem is that they have very much "grown together", and that separating seems an impossibly large change in their lives. They are constantly bickering and, to me, seem less than happy most of the time.

I would very much appreciate input on how to be a good brother in this case, and how to support my brother if their relationship should fail. -My- main problem is probably that I think I know best. It's their lives, so perhaps I should just smile, congratulate them and let them work it out?
<bot>: Brother thinks babies are the antichrist incarnate, his fiancee think they represent ultimate happiness. They both believe the other will change their mind.