Flyinghigh I am still Not convinced just replacing an outer hub will fix what symptoms you described.
Specifically that both wheels were locked together and rotated together.
That really sounds like a spider gear problem inside the center differential pumpkin, Not an outer hub problem.
A bad locking up outer hub would lock that sides axle shaft forcing the driveline to rotate if the other front wheel is rotated.
If the tractor is parked in 4x4 attempting to turn either wheel will not be possible since one side has been jammed and the front driveline is locked because the engine is off but front drive is engaged.
Really think TYM should have expedited a 'complete' and tested front axle install which has not had metal debris circulated through it.
I Feel Real bad for you and especially dad, with this fiasco. Months waiting for parts on a Brand New machine you folks put virtually no hours on is ridiculous.
I actually think you have made the right move getting legal representation going forward. Whatever you and dad end up with, I really Hope it is a great comfortable and reliable tractor from Day 1.