Well thats a different story. Personally I'd limit myself 1 but if sufficient water changes and/or skimming going on, you might be able to get away with 2. To my recollection, coral gobies (
Gobiodon sp.) have indeterminate sexes when young but mature into either a male or female. I have also read that they are simultaneous hermaphrodites, choosing to reproduce as either a male or female. At any rate, to be safe I'd try to get some that were on the small side to make sure.
Aaron