8 bodies currently marked, I think you guys can do one more turn of just one by one. Once we've got all or almost all of them marked, I think it would be safe to have Venn do a sweep with his Icy Vortex. One by one with all the bats and both of you should be effective enough until we can presumably AoE the entire last swathe of all the marked targets.
As for cleanup, considering that they're mainly groundbound and we have spammable ranged attack options I think that it's safe to say that it would be fairly rudimentary and probably unthreatening assuming that Legion wouldn't still be adding to the mass of them. As long as we don't have deal with that part round by agonizing round. That's for afterwards though.