Funny how it never occurs to these people that if they have an extra 6 people hanging out all day, they are using your utilities, toilet paper, soap, dirtying towels, probably helping themselves to the coffee and tea and whatever other goodies you provide, and this is all supposed to be on your dime?
I do have a friend who attends a family reunion once every few years, which happens in a different part of the world each time. One of the group always does the bookings and they book big places that sleep 20 or more. The guy who does the bookings always talks to the host to let them know they can't give an exact guest count, because some people say they'll come, but then can't make it, and some who say they can't make it do end up coming. Some show up for only a couple of days, some stay the entire week. But as far as I'm aware, these are giant villas and they don't charge by the guest, but for the whole place and they aren't at all cheap.