1994 Mazda Protege brakes freeze upl

My son bought this car recently. After 15 minutes of driving brakes froze up and were smoking hot. Car was towed and front pads, calipers and lines changed. Rear
ebrake cable changed, rear drums and shoes checked.
same thing, when brakes begin to heat up engine works harder until brakes freeze. After an hour or so brakes cool and release. Also when brakes are cool, pedal goes down about half way, as brakes become hotter, pedal becomes stiffer to push. 2 different mechanics have checked car and both have no other suggestions.