1995 Ford Taurus brakes dragging after parking brake cable

I'll be grateful for your advice on my 1995 Ford Taurus station wagon's brakes. With 118,000 miles, we brought it to Midas for an oil and filter change and general inspection. We didn't feel any problem at that point, just that it was time for an oil change and inspection of an older vehicle (ours since it was new and generally well-maintained). The mechanic reported no problem. The next day I noticed something hanging near the left rear wheel and found that the brake pedal was bottoming out. I was able to stop by repeatedly releasing and depressing the pedal. I limped over to Midas. The steel brake lines had rusted out and were leaking, and the parking brake cable was broken.

Midas changed the brake lines, rear rotors, rear brake pads, the master brake cylinder, and the 3 parts of the parking brake cable. The mechanic warned that the rear calipers might also require replacement, but after completing the work the next day, he said that he was able to keep them. The bill for parts and labor came out to a little over $1,600.

When I drove home, I felt very little parking brake effect when I tried it on a residential street at low velocity. In addition, the brake light stayed on, and when I parked, the left rear wheel area was hot and smelled of very hot plastic.

Returning to Midas, the mechanic reported that the brake fluid level was fine. He loosened the parking brake adjustment and now reported that the parking brake pedal's return spring was preventing the pedal from returning all the way up, where it would turn off the sensor for the light. He recommending unplugging that sensor's connector. I agreed after he assured me that low brake fluid pressure at some point in the future would still cause the brake light to turn on. He said that the parking brake pedal return spring is a dealer part that he could install if I brought one from Ford, but he also emphasized that the pedal's failure to return to the normal position is not functionally important.

I drove home and felt no parking brake effect at all. After driving about 10 minutes at highway speed the next day, the left rear wheel smelled extremely hot (hot plastic smell again). After a few hours, I drove it slowly to a second Midas shop, close to my office. I asked for a fresh appraisal, including evaluation of whether the overheating might have warped the new rotor. The mechanic here said that he found the rotor ok but I needed a new brake caliper on that side. He spoke with the first Midas shop, and I brought the car there for that replacement ($300).

Driving home afterward, the parking brake pedal effect was again barely perceptible, and now the right side rear wheel is extremely hot. That's where we are today. I'm guessing that Midas will change the second rear caliper tomorrow.

So my main questions are:

a. Is this picture generally plausible? Did Midas appropriately change the master cylinder and initially try to save me some money by keeping the old calipers?

b. Is faulty installation of the new parking brake cables possibly the underlying cause of the repeated overheating? The mechanic tells us that the parking brake is integral to the caliper, so we have to change the caliper if it fails to fully release. But with the parking brake pedal also failing to return to the normal position, I wonder if a single problem might more likely account for the entire situation. Could the cable be pinched or kinked somewhere or otherwise be hanging up somehow? Or could a bad return spring at the parking brake pedal be the problem, so that replacing the rear calipers might not actually be necessary and might fail to solve the problem?

c. Are the prices Midas is charging reasonable?

d. Should I still be concerned about warping of the new rotors from these overheating periods?

Your guidance on this frustrating situation would be very helpful. Thank you in advance!