It sounds like a time for a lot of conversation and compromise.
I can see the fun in being one-on-one for awhile. We find it to be a lot of fun to swap partners for dinner and sit at separate tables, not letting the Maitre 'd know how the marriages really work.
But one of our rules that has never been compromised is that we
always sleep together.
Of course, y'all can do anything you like but I see some jealousy here that could result in unwanted drama. Still, if the couple are as perfect as you say, it's worth a lot of effort to enhance the understanding in such a way that all will be comfortable with the result.
Don't hold back; tell them all y'all's misgivings but stress that y'all like them a lot and want to work this "challenge" through. It y'all can't come to an understanding, as Mrs. Alura would say, "It was not meant to be."
Edit: We'd also stress how important truth is to us.
Good luck, and please keep us informed as the situation developes.
Mr. Alura