I am the father of the bride. We have received several invitation responses, but a very small amount to date, with added guests that were not listed on the invitation, so far one on our side and four on the grooms side. What would be the proper and polite way to inform invited guests that the people they invited themselves are not welcome? And also how do we notify the grooms parents of the situation? Do we contact those people or let his parents handle it? Are we wrong in notifying these people that they cannot invite there own guests? I wouldn't think so.
I still find it amazing that people do not understand that the formal invitation will list the names of the people invited, and only those invited, and that it is rude to add more guests to their response card.
If financially and physically possible to include additional guests then possibly you could overlook a few extras?
If this is not possible, you may telephone the guests and politely let them know that, due to space limitations (or whatever excuse you'd like to use, even financial limitations and considerations) only the number of guests included on the invitation can be accomodated. Be polite, but honest.
You could call the future inlaws and explain the dilemma. Hopefully they will call their family members and/or friends to let them know that you can only accomodate the number of guests included on the invitation. Ask them to get back to you with the exact number of guests attending after they have made the calls. Top Wedding Questions Forum Moderator - "Write your sorrows in the sand, your blessings in stone".