the fact that they are in a 30 gal. tank doesnt matter i've seen a fully grown pair spawn in a 20 high and thats even worse. they are still very young and at that size its not an issue . its not uncommon for gts to do this i had a few that would want to pair up with their male sibling then when i introduced another male the 2 females killed him . mind you he was atleast 3" bigger then both of them. just give them time to bond and be patient.