son of dad's = all his brothers
Now unless you give me the context I can't explain the rest.
But no son of dad's was going to be disabled . In this phrase he is "reporting" the intentions of his father. That is why it is in the past (is going to ... was going to), and the actions of his father follow that sentence making everything clear. It's a very dramatic way of expression the intentions of another person, and I don't recommend it in daily use.
But no son of dad's was going to be disabled. Think of it as "reported intention". (Bit weird, yeah.)