I suggest you not try to separate them with your hands - a riled cat can easily scratch and/ or bite anything nearby. Use a water squirt bottle.

I also find it helps if I can distract / scare them: a loud stomp on the floor near the bed (why they think under a bed is a good place to fight is beyond me). Bang on the wall and holler. Or just spray the water bottle at random under the bed, moving your hand from head to foot and back again. "I" become the big bad enemy and they can no longer focus on one another.

It doesn't prevent the fight, but it helps to stop the fight.

Seems like Crystal and Tommy have a spat now and then - usually middle of the night! ARGH!