I would quest with the priest, but have the pally on follow and only heal. No pally attack or mage attack. You get the most exp if they aren't in the party and if they don't do any damage. Maybe judge light or wisdom if you can (not sure about levels) so in case the priest has to attack it can at least get healed or mana for free. It might take a little, just don't worry about it, a few levels won't be that long.