Okay, no, you don't want this, @Alesia8 . How do I know? I used to let extra people set up their tent around our treehouse listing.
I stopped that. It gets out of hand.
They will all use your facilities and towels and supplies but don't want to pay anything because "we brought our own bed", the tenting people will end up indoors anyway, they find it not private enough because the in-laws are just beside them, and they ding you on stars in the review as if their father-in-law's snoring is your fault.
Don't break your own rules! It's just a nightmare of you being walked all over.
I was finding that every time - I think there were three times? Maybe four? - I let a larger group bring their tents, they were nothing like me and my friends when we camp. They were awful.
Here's a sample reply you can use if you like:
"Sorry, Bob, but we just aren't set up for that. I realize this means you will be finding a suitable listing for your holiday, but I understand completely. Thanks for asking, and all the best!"