There are 4 supports total, one mounted in front of the engine at the top with the letter "L" shaped metal thing bolted to the front of the engine block (near where the timing belt cover is), one at the rear and is mounted to the top of the transmission, and one on either side of the engine.
Most probably, what's worn on your car are the ones on either side, not the ones in front and back. Those are vibration dampers/isolators and look like donuts on lollipop sticks (only bigger). If I were you, I'd replace all 4 of them all at once since by experience (I've gone through 4 Galants, models '87 to '93), when one of them goes, the other follow close behind. It would save you a lot of time if you changed them all instead of doing it one at a time.
If you're a bit short on budget, and if you can live with the noise and vibrations it'll cause, you can just leave them be and wait until they all break down. The engine won't fall out anyway regardless of how beat up your engine mounts are. It'll get darned noisy after a while though...