I dont know what spec your locks are but if you get improved voids as two pets and imp as third you should be able to do ramps BF , slave pens, mana tombs, etc.
i ran 4 locks and 1 shadow priest this way. (pvp server) did most of lvling in instances. Make locks afflic heavy and you may have to drop imp on some of bosses and make one priest heal voids but it is doable. with right spec