So, what is the Son - your cousin - planning to do?  If he continues to work for Dad, hey, it's on him.

If Son walks now, what is Dad going to do?  In mid-60's, if his Son walks, can he continue to farm 600 acres on his own?  Has he thought about that?

What is the Son makes an offer to rent some land from Dad, and start on his own? It's a thought I had.

In 40's is not too late to start over - whether it be farming or some other occupation.  Make sure your cousin understands that.  It may not be what he wants. But right now, this is the hand that he is dealt.