I used to put four bikes on top of a 4 x 4! It was a real bugger! Got more of a workout getting them up there sometimes than I did on the ride (family rides! Pah!).
One problems is if you have the cr@ppy
Halfords Exodus cycle racks*, their crap design makes it doubly awkward. You get the bike up there, then you have to lean it over to get the support arm around the crank, as you do this, the front wheel flops round, the tyre jumps off the carrier, and the bike falls on your head. It does this around 5 times before you manage to get the damn thing on. Especially when you're trying to get the stupidly heavy kids bike in the centre, and there's no clearance under it.
In fact the more I think about it, the more attractive a tow ball becomes, even despite the £200 (plus the £300 plus for a decent towbar mounted rack). Only thing which put me off is changing my car so frequently. Other solution is never take family and bikes anywhere, or only take eldest son with 8kg road bike. That's the solution I've settled on for the moment, it's working a treat!
* Thule 591 carriers can be obtained at large reduction at the moment, around £58.