If you tried the c-clamp, you may have just bought a new caliper. You MUST turn the piston in. DO NOT USE A C-CLAMP!!!!!!!!

 

alright, I did use that tool and I can't get either of them to budge. So my conclusion is that both rear calipers probably went bad at different times and we're only finding out now because we're doing her brakes for the first time since she's owned the car (second time rear brakes have ever been done if that...) I'm almost certain the calipers are bad.