I do not think this is your problem, which is good news if I am correct. I will share my logic and maybe we can stimulate some thought and conversation.
Suspension is a system of springs and damping. The springs absorb the inpact and the shock absorber stops it from bouncing forever (damping). I sounds like your shock absorber is bad.
The hydraulic leveling with the accumulator air bag can be easily checked out by throwing a couple of adults in the rear while the engine is running. If it "pumps up", you are ok.
I hope this helps and that you enjoy the car!