Advice on Changing Pads in a Parking lot

I would simplify the diagnosis, front end up on stands,hard push on brake pedal,then go spin the wheels. That will give you a clue if anything is hanging up.
Another thing, but not likely with your calipers is the pads themselves sticking in the calipers. If the worn out pads came out with little difficulty then thats one you can rule out.

Something else to consider,the quality of friction materials. White box brake pads (no name brand) dont stand up very well, also doesent explain premature failure.