James was killed because he was stalling time for lilly, he stood in Voldemort's way, so he killed him. Lilly was NEVER a death eater, both lilly and James were loyal to Dumbledor, and always were agenst Voldemort. Lilly was also standing in the way of Harry trying to protect him, and because of the prophecy Voldemort wanted to kill Harry. With Lilly standing in the way Voldemort then decided to kill her too.