Try this: "Thank you so much for your offer. You are very kind. We actually have a little family rule that our dinners at Couples are only the two of us, since we get so little alone time at home. We'd love to meet you for lunch/drinks/snorkeling/fill in the blank tomorrow, though."
We have that same rule at Couples, and it's worked very well for us. The only exception to that is the repeaters' dinner and the beach party.
Ragnar Relay 2014 - MIAMI to KEY WEST!
Marine Corp Marathon: 10/12 4:09
NYC Marathon 11/6/11 - 4:21
Chicago Marathon 10/10/10 - 4:19
Marine Corp Marathon '09 - 4:26 / '08 - 4:28[/FONT]