[Ugaya]

SPOILERS

I think the answer depends not only on the experience of your party but on your available spells.
If you have Breach and Haste you will finish them quickly. Cloudkill also works great. Try silence (have it memorized two/three times).
Have you tried hiding your thief and backstabbing. At least the second mage will be killed by a successful backstab.
If you close the door, they won't come after you (one of the major flaws of SoA's AI), so you can try backstabbing several times.