There’s no easy way to make out the barbarian leaders while they are running. No one is giving commands etc. and they’re all humans, mostly men.
Benlin, returning with Rubius (while the archons are dropping rocks) casts Cometfall into the center hunter of men.
Creates a boulder which drops, not effected by anti magic (no SR). Everyone in a five foot radius takes 15d6 damage reflex for half and those that fail are knocked prone if they survive. Also creates a heavy debris field to slow any who have to go through it.
Asinjin and more importantly Rubius, spot the barbarians to see who reacts differently and might be in charge.