Whatever the case, Ash is alive because trap/herm Ash doesn't have pure-blood-male endocrines. As for why the boy twin died, again, it's because they begin to go through puberty before they're having sexual partners. To survive, they'd have to start having sex before even having the full range of motivations and desires needed for sex. In otherwords, a walking rule 7 violation where a 8yo twin went around trying to bang all the MILFs / siblings. The innocence factor just makes that impossible. By the time you're realizing that your hard dick needs a soft place to snuggle into, you'd be dead, as a male on that island.