FI's cousins have teenage daughters (all under 18) and we'll be addressing the invitation to "Mr. and Mrs. Smith, Jane, and Sue." We don't need to include +1's for the teenage daughters - or DO we? Our wedding is out of state from them, and surely they're not going to put their teenage daughters' boyfriends up in a hotel, right? I mean, if the parents called and asked if they could bring the teenage boyfriends along, I wouldn't say no, but it seems a bit squicky to invite them... to me, at least. If they were over 18, that would feel different to me, probably even if they were local it wouldn't weird me out so much.
Is there a rule about this?