It all really depends on the size of them. If they are still juveniles, they will figure out who needs to be who
. If the environment lacks a male, a juvenile's hormones will kick in and the fish will grow and assume the role of a male. If the environment lacks a female, one will become dominant and grow into a female. If both roles are already filled, other juveniles will remain forever so until one of the roles is needed. As mentioned, if you already have 2 large clownfish, they are most likely already female, this is why it is always best to buy them as juveys.