I like to start with using the hydrolics on the car to move those pistons before I disassemble anything but yours is the method I use on a stuck one off the car.....a piece of wood and compressed air. I keep the caliper complete and stick a piece of wood inside where the pads go to keep them from flying around the shop. Once all 4 pistons are broken loose, then disassemble them. I have had a few that won't come loose with just air, so a combo of grease gun and a thermal wrench (torch) will do the trick. Also, sometimes pressing them in further will free them up.