I have two fairy wrasses (labouti and rubyhead) in a 90g with a firefish and no problems. They ignore each other.
A bit over a year ago I just had the rubyhead in with a firefish, clown gobies, orange spotted goby in a 55g. No problem either.
Of all the fish I have had with the fairies, the only problems I had were between the two fairies, not between a fairy and any other fish.