Here's my two cents worth...
Last May we stayed on property at POR, in two rooms, with another family we spend a lot of time with. This May we are sharing a two bedroom at SSR with them for 4 nights (they fly home at this point), then sharing with extended family in the same room for another 3 nights. While it may sound complicated, and it may not sound like an "ideal" situation, I have to say that I am quite excited about it. The families get along quite well and we have different activities planned out for everyone (guys will be golfing three mornings, gals at the spa, kids at the parks and adults at DTD, etc) so that while we may be together for a majority of the trip, we will get some time alone.
I think that sharing the room would be a geat experience, if your families get along well and have had success trvaveling together in the past. Perhaps we are just lucky, but I think that our family thinks of these friends as an extension of our family unit.
That said, when it comes time to discuss the money, that has to be totally up to you. They could do a number of things to "make up" the cost, like buying dinner or groceries, paying for the airport transfer, etc. Or, if you're really feeling generous, you could just use your points and avoid the awkwardness of discussing the money. It's a completely personal choice and I wish you luck!
In any event, have fun and don't worry so much about the awkwardness of your friends staying with you, it could be quite the adventure!