We carry two adult bikes on a front rack. Wouldn't want to carry four bikes there for several reasons: visibility, support weight on the hitch, bounciness (sp?).
If I had to take four bikes I would purchase Dahon (or other brand) foldup bikes with carrying cases. They foldup into a suitcase size which can be stowed almost anywhere.
We used to carry Dahon's on our sailboat and put hundreds of miles on their three speed model.
Camping World has several models. For riding around the campground the single speed should work. For more ambitious riding their multi-speed models would work better.