I was kind of disappointed the Warriors of Darkness fight wasn't a Trial... They could do a Mistrel's Ballad for it.

Make them amped up versions of the normal skills of their classes
Have the BRD and BLM target random people (both target the same person, switch targets every so often)
WHM either doing some minor healing or attacking, maybe use Esuna to get rid of DoTs on the others and sleep a random person with Repose every so often.
Since pretty much all trials are 8 man, to make use of both tanks make the WAR and PLD tankable and give both a tank buster that together would instakill a single tank.

Maybe use their Echo for phase swaps, when one of them gets beaten down they all heal up and change tactics.