Many, many year's ago at a NPS campground in the Lake Tahoe area,(Fallen Leaf) some of there half round pull thru's would easily hold 3 RV's or more(we had my 37'DP towing a car and my friends 33'trailer/tow vehicle with room for another whole set up) and it seemed at the time they welcomed this arrangement. Subsequent year's following this, they absolutely refused the same combinations...Go figure!!!
As has been stated, it's a general observation, that one RV per side is the norm whether its an official rule or not.....exceptions are always possible but don't bank on it!