Original problem and likely present issue could be brakes badly out of adjustment. Sometimes backing up a few feet will let them unlock, though that is not a solution.
Sounds like your past due for pulling the drums off, checking everything out in there and perhaps replacing and rebuilding it all. At a minimum you need shoes with good dry lining and plenty of it, no broken or missing parts, and wheel cylinders with fresh cups and no internal rust pitting, new ones might be easier or even required.

Also the steel and rubber lines should be in good shape.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-