How do I free them up? these are seized.

Tar

Remove calipers from car, separate them, block transfer port with a rubber pad (or a ball bearing) held in place with a G cramp.

If they're not seized too hard, compressed air may shift the pistons, but wrap some cloth around it to prevent the piston from being fired into the distance.

Otherwise, hook up the assembly to a spare master cylinder and pump the piston out.

ken.