Uninvited Guests to a 3hr movie with baby,when invitations said Limited seating for only you and a guest?

I am having a Mother /Daughter Gone With the Wind party and sent out invitations that said their name an a guest are invited to a limited seated viewing. I called to confirm they were coming and one of my friends said Oh yes I am coming and so are my friend, my daughter and her 5mth old baby. I said "But I specified limited seating I only have 8 seats", she then said" thats ok we will figure it out."I dont know what to do, I dont want to be rude and I do want every one to have fun. But more people that expected an a 5 mth old baby for a 3-4 hr movie. Please let me know the nicest way to handle this.

Tell your friend that she can only bring one other person. And you would like for her granddaughter to not be there because it is an adult party. And you want to have a fun time. Even though everyone loves babies, they aren't there to babysit, but to get away from that sort of thing. Suggest that her daughter and baby come at a later time, so you can see the child. That wouldn't offend her. And hopefully she would understand.
Wow that was horribly rude of her.

how rude of them to invite others despite what your invitation said, and even ruder that when you pointed it out they were bold enough to say we would work it out. shame on them. it is your party, you were specific in your invitation. you now have every right to say no, you can't do that. and when they get mad consider yourself lucky. now you can invite somebody who wants to be there, exactly in the manner in which you asked. :)

Somebody please tell me what the hell is the point of a Mother-daughter party where the guests are not allowed to bring their children. Seems kinda like a HUGE contradiction.

No matter HOW you say it...it's gonna be rude...cuz bottom line is: YOU ARE BEING TERRIBLY RUDE!!!

That is really rude. Send her a note cancelling the movie day. Don't invite her to anything again.