HI - I started with three and now have two which are a couple now. The trio was very peaceful for about a month or two. Then two of them started to shack up and hang around together leaving the other to the other half of the tank. I'm assuming it was the male of the pair, but one morning I noticed it chasing one and by next morning it was dead.
So in my case, a 40 breeder, three was probably not a great idea (soft corals abound with rose bubble tip anemone's). I don't know their sex so just got three healthy ones from the LFS. Great color. Eat very well. Do not bother any other fish. Just for whatever reason I ended up with a pair that hit it off and decided to harass the third until death. Maybe a larger tank would have been ok.