gender-equal means also including people who aren't male or female (i.e. nonbinary people). if these hypothetical people are from far enough into the future that they have time travel, they'd know that. so in the spirit of that: Kopaka and Tahu are guys. Gali and Pohatu are girls. Lewa and Onua are nonbinary. (although honestly, if i had my way, Onua and Tahu would also be girls....)