Moon and Ocean: I’m guessing that the moonshadow elves and the ocean elves are dressed similarly because of the connection and the influence the moon has on our ocean (push and pull).
Sun* and Stars: They’re also also dressed similarly, the sun is a star after all.
Sky: The elve has wings.
Earth: That leaves the one dressed in red to be Earth (has the most gorgeous design btw).
*Soren mentions “sunfire elves” in ep1. So it’s either the one on the far right (because moonshadow/sunfire) or actually the one next to them (meaning Earth) because of their attire (red). 11 more days till we hopefully find out.