bl0v's feed

This is what I understood.

1) There are two ghost.
-Ghost 1: the student that died due to bullying
-Ghost 2: The bully that was in the army with MC
2) Both the Ghost possessed the bullied student's younger brother (poor kid)
3) MC exercised the 2nd Ghost.
4) The 1st Ghost still possessing the younger brother

What I don't understand is why is the 1st ghost trying to kill his own brother.