I am with Bear all the way on this one. Yes, the tires should have been off the ground for the brake adjustment. That is easy to do too with the trailer jacks right by each tire. You will probably want to jack it up and give them a spin to make sure you don't have one dragging too hard.
Likely though the brake squeal is the brake controller is now too highly set after having them adjusted. The brakes will generally work notably better after an adjustment so backing off the brake controller generally follows.
Cary