Clowns are really pretty strange little buggers. They are all born male, and the dominant fish becomes female. If she dies, the next dominant male then becomes female. Talk about gender confusion
If you got three small ones, there is a chance that things would work out ok, but it would be much better to have them in at least a 55 gallon in case they don't work out well. That way, there may be enough room for the outsider to have his own territory. It is almost impossible to net a healthy fish from a reef or FOWLR tank.