I just got an idea....since there was a video about Abel....one of Adam's sons being a metalhead in a video on the Hell is Forever metal cover animatic....

That's gotten me thinking....

Since Abel is a metalhead....

What if Cain is a jazznik? 

Even though Abel is an angel and Cain is possibly a demon....it could work. 

Adam is an angel....or was an angel and he's a rockstar mentioned in the Hell is Forever song and Abel is an angel and he's metalhead.

I feel like there would be some favoritism between the sons and Adam. 

There was a quote Adam gave Alastor during the fight. 

"Did you know that jazz is for p**sies?"

Since Cain is a fan of jazz, he would possibly neglect him and favor his other son Abel because of his love for metal. 

Also makes sense....in the story of Gensis it shows Cain was always jealous of Abel due to how his offer to God was to bring the firstborn of his flock of sheep while Cain's offer was bringing fallen fruit off the ground. 

Abel's offer was deemed worthy over Cain which caused Cain to murder his own brother out of anger and jealousy. 

In this case, this kind of jealousy and anger would carry out Adam's favoritism between the two sons.