not tried the side by side carrying of bikes but I have fitted 3 bikes (including 1 DH bike) riding kit and 3 people in one without a problem.
The last of the 2004 models Grand Cherokee limited had a split rear seat in a 2/3 - 1/3 format which folded down quite well however the head rests did protrude into the flattened load space.
I never tried to remove the rear seats however if you did manage it you would lose the flat platform that you get when you put the seats down. It is a bench seat picks up and goes forward, rear backrests fold flat affair save for the previously mentioned head rests.
I have no idea if you could camp inside it with the seats down, probably but you would have to curl your legs up - not the biggest fan of camping so I never looked at the possibility.
Diesel 2.7 CRD 5 cylinder engine was a little rough and not the most economical of things, driving down to France with a full load (2 people, 4 bikes, 2 weeks riding and normal cloths, full set of tools, a workstand and spares) sitting with the cruise control on 75 I got about 31 mpg according to the onboard computer.
When there is nothing in it the car really doesn't ride that well, it kinda oscillates down the road.
The last 1/4 of the fuel tank seems to have less capacity than a thimble, blink and you will wonder where all the fuel went.