Size of property & resources would dictate how many you COULD handle. More people are normally better because more skills. There has to be cross training.
To make things fair for all, each family has to be responsible for their own shelter & meals. Someone might bring a tent & someone an RV. One family might have rice & beans only while another has a load of FD foods. Same goes with each family & their water stores.
There still needs to be a commons area where meetings & various training is help. Water, wood, & light will be needed for this area as will resupply. Also, some food stores for long training sessions that instead of lengthy break for everyone to go to their camp to make some food be able to do something like a big pot of stew.
I would set minimums that the group can agree on. Like number of firearms for each adult & ammo. Minimum amount of food they must bring like one week, two, a month, etc.
Depending on the amount of property avaiable, I would assign each family the same amount of space. But separate those with generators & those without. And a curfew when generators can no longer be run.
And I would set up pre disaster a monthy fee which would be used exclusively for the commons area.