It seems unlikely that both front wheel cylinders would freeze up at the same time. Unless the car has been sitting a long time.
Try pulling the front drums so that you can inspect the front shoes and drums. While you have them off, hit the brakes gently. You should have little resistance since there is nothing to hold the shoes back. If you can witness the brakes while the pedal is being pushed that would be better.
Most cars will lock up the back brakes under extreme braking, because most of the weight is transferred to the front. An adjustable proportioning valve can be added to change the point at which the back brakes lock up. However, under "normal" breaking conditions, your front brakes will be taking more of the load causing more heat & wear to those parts.