What do you do when a person you invited to eat at your home invites another member of her family without asking you?

I invited a couple and their daughter, and this one lady for dinner. Just found out the lady is bringing her son and I never knew it until today.
It would be fine, but there are six now, and I have a round table for 4 people. I can add another chair for 5 but it’s not very big, the table. About 48 inches across. So I guess two people will sit on the couch to eat. Am I being too fussy?
A note: the one who invited her son now once overstayed at my home. We went to lunch at 11:30, came back to my house to watch a bit of tv at 3:30, and she left at 7:30 when I had a class at 8:00. I never had her over again until this weekend. So

in my invite I said it’s from 4:00 to 7:00, just in case she decides to stay too long again.

What do you do when a person you invited to eat at your home invites another member of her family without asking you?
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