They are still juveniles. When young, most fish whether schooling or not stay together for safety. There will be a certain point where they no longer feel the need for this group safety and one or more of the fm's might get seriously picked on and/or hurt.... keep a watchful eye on them as they grow.
as stated previously they are not a schooling fish in the truest sense. I have 6 in a 55 gallon tank. the smaller 4 of them tend to hang out together while the other 2 tend to go about their own business.