[Wumpspawner]

My approach to this was to set up what I like to call a 'meat grinder.' Before you make the interactions that start the fight, group your party together in the hallway to the north, tanks in front, weak ones in back. Have some good area affect spells/devices at the ready, such as fireballs, potions of explosions, arrows of detonation, etc., have a missile weapon on every charcter, and have the aforementioned tank with boots of speed ready to go as well. Haste your entire group. Now send your hastened tank with the boots of speed south and do the talking. This fellow is the lure. When combat opens up, have him haul ass north, making no detours, and the warders will chase him. Use your area affect spells and devices to level the area immediately in front of your party as the bad guys pass through. Your lure will be going about MACH 5, so he should clear ground zero pretty easy. Then take the heavily softened warders down with a hail of arrows, bolts, and stones. Your tanks might have to drop their missile weapons and engage in hand to hand, but it won't last long.