I have a family of 8 6 kids myself and wife are TT sleeps 9 comfortably but I noticed allot of the camp grounds state 6 max per site what do large family's do ?
If it is a commercial RV park, you tell them how many people and they will decide how much to charge.
At public campgrounds, you can either explain your situation or hope nobody is counting. I've not encountered a six person restriction at public campgrounds I've used, more often it is something like one RV, two tents per site, and if a group needs more room they'll take a couple of adjacent sites.