I hope that even though your ex is filled with anger that in his final days a spark of remorse might prompt him to say "I am sorry." Even a little act of contrition can make the passing out of the body easier.
If you can possibly leave space for this, it could make this easier for you.
If not release the guilt and feelings of regret. Somehow you have been given this life situation and you can only do the best you can.
For your children and grandchildren, try to find pictures of fun times you all shared or tell stories of any positive experiences. In this way all of you can release the negativity that could entrap you if you obsess about it.
You and they are survivors.
There is another forum on grief and survivors of abuse here in PC.
http://forums.psychcentral.com/grief-loss
http://forums.psychcentral.com/survivors-abuse/

Our hearts are with you