Guests RSVP for 2 when only 1 name is on the invite...

I think if they are engaged or living together, you should invite them. Otherwise, I would call them up and simply say, "hey! I am so happy you can make it to the wedding. Unfortunately, we have to keep the numbers limited at our venue, so we are unable to accommodate everyone's SO. Really sorry, hope to still be able to see you since you mean so much to us."

Or something like that.

Call them and explain politely that you are very sorry, but you have limited space and unfortunately cannot accommodate more than the guests whose names are listed on the envelope. As long as you're polite about it, they shouldn't be upset, since they made an incorrect assumption in the first place.

@Tatiana very well spoken

Oh Katy I feel your pain! I am using the WW RSVPing area as the only method to RSVP. That way people can only RSVP for who is listed. However, my aunt RSVP'd for her and my uncle (who I have NO relationship with and thought there was zero chance of him attending. long story) I have since found out that my uncle is NOT attending (insert happy dance) however, my aunt has decided to invite her cousin to join her...who I have NO relationship with! And she hasn't even told me! I had to find out from my Mom! What's wrong with people?! I honestly think you just need to tell them. If they are close to you are are decent people they will understand. That's what i have had to do with some of my friends and they were fine with it. Good luck!

Wow, that sucks!! 15 extra, wow. I hope this doesn't happen to me. Good luck on handling it. Let us know what happens.

I would simply call them and say do to the fact that there are limited seating at the wedding I can not accommodate extra guests. The invite was only for you.. That's kinda how I would say it.. Good luck with everything..

Ahh I knew I'd run into that problem. I just ordered invitations and printed __of __ attending. So I can fill in the second line. 1 or 2 depending if they can bring a guest