Rebuilding brake calipers is pretty easy, finding the parts is the problem. I know the front calipers for my '87 are '84 Toyota Celica, not sure about the rear inboard but my best guess would be Toyota also.
A brake caliper just consists of a rubber seal near the piston edge, piston boot and maybe some o-rings sealing the two halves if they split apart. The rear calipers on my car have a 'rotating' piston for the ebrake.
Unlike a conventional caliper where you can just squeeze the piston back into the bore, on this type you need to rotate the piston counter clockwise back into the bore. If you do not rotate the piston it will give the illusion that it is frozen in the bore.
I'm sure Jeff at JAE could hook you up with calipers or a rebuild kit should you need it. Check the cables to make sure they are working smoothly and adjustment is correct first.
Robert