Can you place a tent and an RV on the same site? Still have 6 people

Yes.

Yes, but only 2 tents if you have a recreational vehicle. 3 without.

Yes, there are several sites that are large enough to accommodate that.

Yes, there are many people that have a RV and have a tent or multiple tents. Their policy reads: Maximum of 6 persons per site. More than 6 persons will require rental of an additional site.