Honestly I know what the odds are especially since you looked them up but you may very well have all the same sex. That or you might have one or two opposite sex that just don't want to put out! Meanwhile I have you tried doing a water change with cooler water? Also for some reason if I just feed Frozen bloodworms for a few days straight then mine tend to spawn. At least I think it's the Frozen bloodworms but if somebody told me that then I would say that's dumb. Last thing I can think of is go by a proven female because you look like you have a good number of studs in there. And if they aren't studs then they are some big girls!