the "big guy" looks like a terminal male, and if about 5" big, most likely it is a Supermale (aka Terminal male). the other ones on the pic look like they are transitioning to being a male. "female" HI Flames are notorious in turning into males in our tanks. when I had HI Flames, I started out with 2 small females since I wanted to see one transition to male but as soon as one started transitioning, the other also started. so I ended up with two males and they flashed each other, switching spots on which one would dominate the other. they co existed fine with just the occasional chasing. I had a Supermale Lineatus that ruled the tank and would anyone in their place if he notice the chasing getting too much. so in a way, I think this is how the two male HI flames co existed.
anyway, good luck with them as they are truly one of the best fairy wrasses in the hobby. :bigsmile: