Humanly speaking, it certainly may seem like a hopeless situation, because either your daughter-in-law or your son (or both) are going to have to change—and right now that seems impossible.
But don’t forget the words Jesus spoke on one occasion: “With man this is impossible, but not with God; all things are possible with God” (Mark 10:27). God has the power to change even the most rebellious and hardened heart—and sometimes He does. No one in the Bible was more opposed to Jesus and His followers than the man called Saul of Tarsus—so much so that he decided to dedicate his life to stopping them. And yet one day Christ broke through his spiritual darkness and rebellion, and from that moment on Saul—later known as the Apostle Paul—dedicated his life to the spreading of the Gospel.
Pray for your son and his wife, that whatever is causing them to act this way may be overcome, and replaced instead by love and respect. Pray most of all that Christ will become the center and foundation of their lives, for they need His love and peace.
In the meantime, do whatever you can to let them know you care about them and their children. Life isn’t always the way we wish it were, but with Christ’s help we can learn “to be content whatever the circumstances” (Philippians 4:11).