Hello,
Definitely you can file a divorce on the ground of cruelty.
Since the crime has been reported once therefore it will be easier for you to file and prove the case.
Make those boys also a party to the divorce suit.
Also since the younger son is in the custody of mother and is living with her at her place therefore custody case will have to be filed there only.
While deciding the custody, welfare of the child is of paramount importance.
Let me know if Me and my team can be of any help for you. We have our branch office in Bangalore as well
Regards