Sadly, I think your son should seek the advice of a solicitor; according to the facts presented here his wife's behaviour is unreasonable, if the main trouble is that she resents him working long hours to support his family. By her behaviour, she is actively preventing him from forming a relationship with his baby son, and he needs to get regular access sorted out quickly. Perhaps mediation may be suggested; as you say counselling is no use unless they both take part.
What is his wife living on? If she is not earning does she have any income of her own, or are her parents supporting her and the baby? Does she not have a support network of friends, often more use than parents?
As everyone says, don't interfere, but it is difficult for you to form a loving, supportive relationship with your daughter in law if she has moved away and won't respond to your texts. Could you write to her and ask to see the baby? His welfare is the most important of all.