Question about no extra guests

You can write on your invites. “No additional Guests can attend. Only guests that have received an invite, can attend.”
I’d suggest giving no one a plus one. To make it fair with other guests and might stir some feathers as well. Of course do what is best for your situation and wants for your wedding day.

We put ___ of ____ seats and filled in each invite with the number of people included on that invite. So, a couple had ___ of 2 while a family had ___ of 5, etc. Additionally, guests were named on the envelope, or we used _____ Family if all were invited.

It’s considered bad form to write extra details on the invitation or reply card. There are several steps you can take: write invites names only on the outer envelope, contact guests immediately who rsvp for extra guests and let them know you are unable to accommodate extra guests who are not named on the invitation. Also have security which is required by many venues if you are concerned about anyone crashing who is not invited and will cause drama by doing so. Beyond that, there’s not much else you can do unfortunately.

It's actually not polite to put who is not invited on the invitation. I'd advise against putting that part about no additional guests anywhere.

Nicole's advice is spot on.

I am so torn on this subject. I think Nicole has given the best advice if you wish to stick strictly to “etiquette”. However, a lot of people these days are not really familiar with wedding etiquette, and may not pick up on certain things (or may even choose to just flat out ignore them) if they are not expressly spelled out to them. I think this is partially a know your crowd sort of thing. Will your guests understand (and follow) the ____ of ____ seats have been reserved for you? Or will they just ignore it and write in additional people? If you know your guests fall into the latter category, then you could choose to either just spell it out for them or have security at your event who will check off names at the door, and not allow entrance to anyone who is not on the guest list. If you feel most of your guests will understand and adhere to the _____ of ____ seats on the RSVP, and stick to only those expressly written on the envelope, then you could just go that route and personally call anyone who writes in additional guests (and you could still have security at the event, if you think it would be an issue).