I feel for the OP with his issue of having so many persons to occupy a campsite. There are very serious reasons why most CG's public or private have a max of 6 persons capacity and totally agree with that parameter. First off, CG sites are not home sites in size so over 6 persons creates even more noise and crowding and of course much more added cost for the CG and it's utilities too.
We have been RV'ing/camping for 53 years now and also live in West Michigan just 50 miles south of Silver Lake area so often with many of our family and their minor friends along also. We do prefer the state parks as that is where true nature and real outdoors is abundant and so important for kids. We are retired but take grandkids and of course each likes to take a friend along too. In fact we encourage it!
We always took our 2 kids of our own camping and virtually always each had a friend with them too! That already makes 6 on the one site! We do strictly adhere to the 6 per CG site rules and always have. Beyond that 6 in our total party which was so often, we always pay for second site. Why over 6? Because often there was added grandkids and the total group would be 10-12 or even more. A couple times there was more than 18 of just our family members alone but never more than 6 per paid for site. Max was 23. We take out 5th wheel to family camping events.
Yes, there needs to be a camping/sleeping unit of some type on that 2nd or 3rd or fourth site also which only right and we have found that to be the norm requirement also. The older kids loved to sleep in the tents by gender so really made it easy. 2 in a pup tent and later found using a dome tent for 4 or maybe 4 or even 2 tents for 6 total on an added site. Always had a 2-1/2 gal porta potti in there for them too as there was room for it, especially the girls tent, so no need to go the CG restroom at night alone. Where's there's a will, there's a way! So easy to do as we simply pitch a tent on the site. Where do we put the picnic table? As close as possible to the line between the 2 sites which keeps a buffer zone for the other sites on either side and keeps most all traffic in the central area between the sites. That is why we always have 2 sites or more paid for per night for our clan when over 6. If 3 or 4 sites were needed so keeping only 6 max per site, the eating gathering area was always centrally located.
Talking mostly about State Park CG's but several private parks too. Some most used were/are Grand Haven, Hoffmaster, Silver Lake, Ludington, Interlochen, Leelanau, Wilderness, Burt Lake, Hartwick Pines, state parks in the L.P. In the U.P., Straits, Tahquamenon, Muskallonge, state parks. Platte River and DH Day in Sleeping Bear NP. Also Indigo Bluffs RV Park near Sleeping Bear NP.
We still do a lot of large family camping and it's not that hard but almost a must to have consecutive sites reserved well in advance.