Honestly, I had 2 males die as well over a few month period. There is nothing wrong with anyone else in the tank. I suspect they were just weak individuals. That or the females got sick of them pestering them and pummeled him. There were no signs of distress or disease on my fish though.
If your female shows signs of disease, clear it up before adding anyone to the tank. Remember several females to one male. Also, I hope you have a place to bring the babies one they are born or your tank will be over stocked in no time. Over stocking the tank has dangers in itself. High ammonia, death to the fish. Proceed with care.