"If you smack the tires you'll need a heavy sledgehammer to effect some real force." I would advise against this method as the rebound force can do you severe mischief! I guess you left the handbrake on and are now suffering the consequences. They will lock up without that though. Remove wheels, loosen brake adjusters and the hand brake cable and use a copper/plastic/lead mallet or dead blow hammer to beat around the drum. A steel hammer can crack the drum or break the flanges off. If no joy, try some heat. You can also get quite good leverage with the wheel back on. Beware damaging the stud threads if using a long lever.
Fronts can be loosened by prying away the pads with a screwdriver or a wood chisel and mallet. Once the fronts are free you can then rock the car back and forth to hopefully free the rears.
If all stuck I'd start with the fronts first. The 3 puck callipers are very prone to seizing up.