First things first, next time your camper is set up somewhere, have the family go inside and walk around. Look at your wheels and tires. I guarantee you that your wheels are rocking back and forth at least slightly as they move. That is a large portion of the movement that you feel. X-chocks or ONEstep or similar products that put opposing pressure on tires to limit rolling will help reduce movement.
All trailers have flex in the frame, lightweight trailers have more flex. Pooducts like the Strongarms appear to work great in terms of stiffening up a frame. Perhaps adding another set of stab jacks in front of and behind the axles would help too. Other than that, you have to learn to live with a little motion in an RV.
We've been quite happy with the ONEstep system, reducing the wheel rotation. That really cut down on the motion that we feel with 2 active kids... now 5 and almost 3.