Steven et al - I called the place you listed the number for in BigSur,
but their group sites will be closed during the time when we want to
visit.  They do have showers, but they do not have hookups for water,
electricity, etc. in their other sites, and the woman with whom I
spoke gave me references for 3 or 4 other private campgrounds nearby,
which I will call.  Regarding group vs. single sites, even if we
were not able to get a group site at one of these places, it sounds
as if their single sites can often accommodate more than one vehicle,
usually 3, and if there are, say, 20 of us, we could "sort" of
still be together by having adjacent sites with 3 vehicles at
each site, gathering at one site in the evenings for campfire
and mealtimes, etc.  

Will let you all know after I've talked to the other places
that were recommended to me nearby.

/martha