Thank you all for your extremely interesting and informative points of view. I am very glad that I started this thread.
Things that I have learned:
1. The suggestions for the DDs learning about financial planning were great. I'm not the most knowledgable person when it comes to finances and what to invest in (IRA? 401K? Trust Funds? etc.) So I will look for and find some sort of seminar or info-class type of thing that the DDs and I can attend together.
2. None of the people in my OP have a lot of money nor are they firmly established yet in any kind of career, so the fact that they are pretty much starting out on the same foot tells me that there isn't a real reason for a pre-nup. Thank you, everybody for pointing this out . . . building an "empire" together is a big part of the joy of marriage. Just because the DDs are probably going to inherit a hunk of change doesn't mean that the BFs are going to depend on this windfall for future planning. Who knows? They just might have pride enough in themselves (and it seems that they do) to be frugal enough so that the couple can afford to buy a house on their own. On the flip side, I have no clue as to whether or not the BFs families have money. Maybe they're looking to inherit more than the DDs? But that's none of my business.
3. I agree on this very important point: couples should do their financial discussions before marriage. Should one paycheck be put into savings and use the other on every-day life? Should each person put 1/2 their paycheck into a joint house account and the other half be their own personal money? There are many ways that this can be worked out but the agreement of how finances will be handled should be made before marriage. Of course, any agreement should be pliable enough to cover emergencies, etc. Marriage is, after all, an equal partnership. When the "M" word becomes a permanent subject I will gently ask/coach the DDs that they make sure the finance (along with the "do you want children?"
) questions have been discussed.
4. Nope. Not going to do it. I'm not going to tell the DDs that they are probably going to come into some money. Let them forge ahead on their own with their own wits and knowledge that they have earned by themselves.
Again, I thank everybody that posted. Reading this thread was quite a learning experience for me.