I am sorry to hear of your troubles with your son. From your letter, it seems to me that your son is fuming with anger and this started in childhood. He has shown a history of inappropriate behavior and he apparently has brought this anger into the marriage. You are correct: If he does not address that anger and take steps to diminish it, this will affect all of his important relationships, including with his wife, with his own child, and with you as his father and with his own mother.
If he refuses to forgive, then take it slowly with him. Forgiveness cannot be rushed or demanded. He will have to choose it for himself by being drawn to the idea of forgiving others. He may need to forgive his mother for over-indulgence. He may have to forgive you for your deep anger toward him (as you practice forgiving him). And he and his wife need to engage in forgiving and receiving forgiveness from one another if they will save their marriage.
If your son refuses to forgive, remains furious, and places all blame on others, he could be suffering from narcissism, especially if he was over-indulged when growing up. He will need to see this narcissism, practice humility, and even work on seeking forgiveness from those toward whom he has been insensitive.
This is a long list of forgiveness themes. I recommend that your start slowly and see if your son is able to consider forgiving his mother. At the same time, you should consider forgiving him so that your interactions with him are as supportive and loving as possible. See him as emotionally wounded rather than as a big problem for all in the family. This perspective may assist you as you begin to forgive.