As long as they arent too large, I think you could probably get away with them in a 120. I have a 300 with lots of tangs, and after the initial fracas, they all get along fine. The key is enough live rock that they all have a place to call their own, where they can be in one section of the tank and not see the other fish on the other side, but you still have to leave enough room for them to swim freely.