You may want to spawn the golems first before clearing the mobs, so that the ??? doesn't disappear while you clear the area.
When ready, target the ??? to spawn 2 NM Golems (Mokkurkalfi).
It is possible to pop them with Sneak active so that they don't aggro, even though Golems normally aggro by Sight (confirmed three times). You can then pull them with a ranged attack and fight them one at a time.
It is actually not necessary for the mission to defeat both NMs.