Kill Artruis the Heartless. While securing the aid of friends is highly recommended, Moodle will not be able to accompany you on this task.
Perhaps the crystals will ward off the undead gradually, but there is one more thing that must be done.
We need to find the leader of these undead and kill him to ensure there's no one to push the wretches back upon us. If my suspicions are correct, he will be somewhere inside the fallen pillar... the Sundered Shard.
The corpses being dragged there would suggest as much anyway.
I'll place the shards and bring the news to Soo-say... you will need to find other help in the meantime.