Sadly, OP, you son has to make his own mind up about what he wants to do and what he can do about his marriage.
You love him, and obviously will tend to believe that the faults are all on your DIL's side, but are they?
Quite a lot of women take on the responsibility of "deciding everything" because when they try to discuss anything from the upbringing of the children to paying of the mortgage or choosing new wallpaper, their husbands just say, "Do as you like, dear" meaning I can't be bother trying to do anything about it.
This may not be the case in you son's marriage, but I assure you that down through the ages many women have been forced to decide things on their own because their husbands were too d*****d lazy to decide anything at all.
Whatever the rights and wrongs of it, no good has ever come of meddling between man and wife. Only you can decide whether giving advice would be meddling or not.
If my son complained in the same way about his wife, my advice would be, "Son, only you can decide what you want to do about your marriage, but your father and I will support your decision, whatever it is, once you have made it."