dddd

I deal with this situation all the time!

Don't take the calipers apart, it's wasted time imo. Put a couple of drops of synthetic oil (like Tri Flow) at the point between the two arms and leave it for a few hours, it will soak in.

The pads are no good, replace.

The cables are likely still good on this bike, just add some silicone lube to the inside of the housings and cut off any damaged/bent ends.
I use silicone lubes in plastic-lined housings and use grease in un-lined housings. These ones are lined I believe.

These caliper's springs are pretty stiff, and relaxing the springs (or using thicker pads to same effect) will effect a disproportionate improvement in actuation ease.

Remove the caliper and grab the end of the spring with pliers, bending slightly inward.
Relax both ends of the spring equally if possible or one end of the spring may tend to slip off of it's return peg on the arm.
Use care and experimentation to achieve the proper degree of relaxation.

Brakes should be hugely improved with all of the above. Black is usually the highest-gripping pad material in dry conditions, but also most prone to squealing (grippy pads squeal more).

These calipers require a 4mm hex socket (!!!) to center. I add a toothed washer (rotella dentata) at the mounting to prevent the caliper going off center as they tend to do.
Don't mess with the plastic knob at the pivot. It's a locking device to help hold the locknuts underneath from moving independently. It is not an adjuster!