[Mike C]

A wobble in the rear is neither. You have something bent. Either a wheel or axle. Swap wheels side to side and have father-in-law follow again. If wobble changes side, wheel. If not, axle.

You can set up a fixture using a dial indicator also on a fixed stand and put the indicator on the axle flange (truck on jackstands and wheel off) and rotate and check runout. Needs to be really level for accuracy, but if you can see the wobble it's way off.