If they have stayed at a Couples before then they are repeaters, they do not need to be a RR member, that said they should sign up for RR now and let them know of their stay, they will not get credit for it. If there are any questions you can stop at guest relations at the resort and let them know that they are repeaters and they will issue them an invitation.
I don't think I've ever heard the word No while I have stayed at any of the 4 resorts, except of course from my husband when I want to buy another pair of sandals from the sandal guy!
Couples Preferred Travel Agent/Couples Specialist
Doesn't Get any Better then Couples!!