Help with seized brake

2005 Acura TL. 105K miles.

Last night when I parked the car in the garage I noticed incredible heat coming from the right rear wheel. I had been hearing occasional squealing from the wheel at low speed. The squealing had stopped when I depressed the brakes. I did some research on AcuraZine and jacked up the car to debug what is going on. The parking brake lever is not engaged. I see that the wheel does NOT turn. The outside brake pad seems heavily worn. So according to the forums, it must be a seized caliper. I removed the bolts holding the caliper and the caliber mounting bracket however the caliper is stuck to the rotor. It moved half an inch but isn't moving any more.

So, I have a few questions:

1. Any ideas to remove the stuck caliper?
2. Is a seized caliper the right diagnosis?
2a. If not, what else could it be?
2b. What additional diagnosis should I do?
3. If the caliper is seized, does it need to be replaced? Do both calipers in the rear need to be replaced? (The car used to be in Ohio so the caliper mounting bracket, the caliper, etc. are definitely externally rusted.)

Thanks