I have the Cougar 2008 310 SRX. 34 ft long 5th wheel. It has a side door and ramp. I would carry a full size quad and a dirtbike. I'm sure someone can figure out how to stuff 2 quads in there. Trailer weight is ~ 8300 lbs dry.
I think that Outback (Keystone) had one that would handle two smaller ATV's. Pull one up the ramp, move it to the side, then pull the other one in. I don't know if they still make it.
ETA - they have a new 324CG that might be what you are looking for. Crossroads also has some that load the ATV's externally on a deck loaded from the side.
There maybe a few out there, they hit the market a few years ago then died off. The one listed above is no longer in production either. Most side loads were only designed for one ATV. The Raptor 384pk is a 5er with wide enough ramp for two though.