How can one deal with a 48-year-old son who never prays, despite constant advice from his parents and wife, and has not responded to all this advice?

This man is committing a great evil and one of the gravest major sins by persisting in abandoning prayer. This is worse than fornication, theft, drinking alcohol, and murder, by consensus. It may even reach the level of disbelief according to some scholars. You must advise him and explain the danger of his actions, and that there is fear for him of a bad ending, while also clarifying the benefits of prayer. If he does not take heed and if he shuns you, then shun him in the hope that he will be deterred. Otherwise, continue to advise him and supplicate for him.