In order to satisfy the elementals, the padjal must make ritual offerings of life-giving aether… or something like that. The excuse you come up with to facilitate it is up to you, OP doesn’t care much as long as the seedseer siblings fuck in weird, ritualistic ways. Bonus points if the incest isn’t normalised and both older sisters are initially uncomfortable with the idea of taking dick from their little brother. Maybe a now deceased padjal like A-Towa-Cant used to fill A-Ruhn’s place in the ritual?

TLDR, Kan-E and Raya fuck the shota.