Dear Jim,
There is no point in pulling his
handsHand or foot spasms
Hand tremor away from his mouth - as you've already seen, this is not useful. The most significant intervention is to diminish the conflict that occurs between his parents. This is damaging to a child. Now, it takes two to tango, so to speak, so while your son is not able to control the behavior of your daughter-in-law, he can control his own behavior and see to it that he does not participate in the arguing or whatever form the conflict takes. This can be difficult, but it's crucial for your grandson's development.
Relative to professional intervention, the best course would be for your son to consult with a child menatl health professional to help him in his efforts to be a good father and deal with this conflict with his wife. It's not your grandson who needs the help, it's his parents.