Ernest and William had a very good teacher student relationship with each other. But, after discovering that William is the Elector, Ernest has decided to destroy William.
Crosby tried to exorcise Sytry.
Crosby holds disdain for Dantalion, who used to be a human.
The two have not interacted as Ernest does not know that Camio is Nathan. Although, judging from his interactions with Sytry and Dantalion, Ernest would not hesitate to destroy him if Camio revealed himself.
Crosby is devoted to Uriel and Heaven's teachings.