Complex sentence: The Glatzels were informed of the Warrens'rather unique skill-set by their priest, who felt that David's affliction was demonic in nature but was unable to perform an exorcism due to poor health.
Split into simpler sentences: The Glatzels were informed of the Warren's rather unique skill-set by their priest. The priest felt that David's affliction was demonic in nature, but was unable to perform an exorcism due to poor health.