Rust on the e-brake cables swells and the cables stick in the case or sheath. It is possible to get sticking e-brake cables to free up by soaking them in diesel fuel. But, if you go through all the trouble of removing them it would be quicker, and less work, to just replace them.
Coat the new cables with a lubricant that will stay in place, eg silicone, red grease, heavy duty bearing grease , anti-seize compound, etc. Coat as much of the cable as you can and work the lubricant into the sheath by sliding the cable back and forth in its sheath.
A common indicator of sticking e-brakes is the dragging brakes. It is also indicated by an e-brake pedal that will not return to its full up position, and the light will stay on. Granted, this can also be because of a weak pedal return spring. But, when this occurs it would be wise to check the e-brake cables.
Also check your slider pins. If you remove them, coat them with a light coating of silicone grease. rangerj