I have two ideas for the evil and Good factions. Let me know which y'all like best. 

One is that the lawful gods were made by the one entity to rule over the universe, and the evil gods were made by a different entity to combat the good faction. Leaving the neutral faction as evil made who don't care what happens. 

Two us that we were all made of the same entity but there was an eventual rebellion and split of the Heavens.