i had a character with high telekinesis sneak around the room and place those pots and jars in front of the circles where the bosses spawn. if you don't leave any gaps, when the battle starts, they'll be stuck behind the jar barricades (jarricades?) and won't be able to do anything.

sometimes the twins-joined-by-fire spawn in front of the jars, but then you'll only be dealing with two bosses instead of the 4.