yes, they will control the little ones, you can kill the big ones manually. After then are done, they will still need to eat and may move to zoos, etc. I don't keep any soft corals aside from ricodea, and thus have no worries about keeping multiple peppermints in my system. My shrimps are well feed and don't bother my SPS or acans. I have enough shrimps that they will control any accidental pest that is introduced. In the past, my foxface ate the larger aiptasia, since they are known to pick on soft corals also. I add peppermints in groups of 6 or 12, so that at least one of them will eat at least 1 type of pest. They all have different tastes and never know which shrimp is the one who's going to help out.