(assuming each enemy can move 1 square this turn and the enemies are all trying to get as close as possible to the player)

You'd have everyone move left, probably. But to come to that decision, you have to make sure (a) top minion doesn't get in the way of middle minion, (b) middle minion tells right minion that it's vacating its current position thus making room for right minion's advance. This will require something a bit more sophisticated than just iterating over all the minions and having them act independently in sequence...

My approach will probably be some kind of score maximizing search problem.