[Pirengle]

When you're making up a party based on a series or something, you don't have to stick *exactly* to the party makeup and layout the series described. You can always invent a PC that rounds out the party (in this case, giving the trio the much-needed thief) and claim for roleplaying purposes that a new character is tagging along.

Or you can go without a thief, make Melegaunt or Galeron the PC, and give them a familiar with basic thief skills, and rely on Find Traps and Knock when necessary.