in addition to the Genome theorys and ideas and facts flying about, we know that they must have males. [spoliers]Kuja and Zidaine are proof of such.Also, didnt Zidane call the one Genome that was to be his replacment if things failed his sister?[spoilers]

It is fact that Vivi is male, for the simple reson that they call vivi male throught the whole game. While, Freya is clearly female because she is refered to as female. Quina, they(being the group) dont know about, so they refer to him/her as s/he though the game.