Oeilvert: Zidane, Freya, Steiner, Quina
Desert Palace: Amarant, Eiko, Vivi, Dagger

You can use magic in the Desert Palace, so I send all the magic users there. Amarant goes along so he can restore their MP with Chakra and provide some physical attacks.

The Oeilvert team is largely physical oriented, so it makes sense for them to go.