[Cerek]

Thieves gain levels faster than any other class, so you would gain the needed skills quickly enough.

However, if you've taken a proficiency in katana, then Dakkon's blade is an excellent choice for a kensai dualed to a mage.

But you're party IS very "magic heavy" with a sorcerer, fighter/cleric, and Edwin. That should provide all the spells you need. This would give you the option of dualing to a thief and then backstabbing opponents with Celestial Fury. {oh yeeeeaah!)