Hello,
I agree with Cynthia. However, if you have a limit on the number of people who can attend the banquet, and you want to make sure you take care of family first, then I personally don't see a problem in limiting the number of friends a family member can invite. Also, make it known that everyone has to pay. I encountered a situation when some younger cousins brought a friend to the reunion, and did not even realize that their friend also had to pay. Well, the friend said that he'll stay in his hotel room during the banquet, since he hadn't paid, but still found his way inside the banquet. Sometimes, people are something else!

Melvin