"he wont admit to me or doctors that he hears voices."
What he's experiencing sounds like command hallucinations. In this case, besides antidepressant medication for his mood disorder, antipsychotic medication is added.
If he is hesitant to talk to you or his physician because he thinks that others will assume that he is crazy, you may want to help hi understand that psychological conditions can cause people significant distress when these are not managed. No one who is well informed will ever say that another person is "crazy". Mental health disorders are treatable like any other condition. So, initially you may have to educate him on the causes about why people may experience something and the fact that they do not have to suffer forever because treatment is available.
Since his spoken to your daughter in law, perhaps the two of you can try and set up an intervention for him at home where you share your concerns about his health with him. You may focus on specific examples of times when he had seemed well and happy to you and then other times when he had seemed tormented and depressed. Point out to him that suffering does not have to go on and ask him if he would be willing to take the steps to get help. Ask him what would he be willing to do to get better. That empowers him and gives him some options to think about. He could either speak to his GP or a psychiatrist. Remind him that his consultations are private and no trained professional makes conclusions such as that he's crazy. They treat the problems that the person (he) is experiencing. Even he is concerned about anonymity, there are some online psychiatric services that he may also look into.
Let him know that you're behind him and if he's willing to, offer to find a physician for him, arrange for appointments and even go to the first appointment with him for emotional support. You can share w/ him that you miss the times that you recall when he had seemed happier and healthier and that depression and other conditions seem to rob him of the things he used to enjoyed doing with you as a couple.