This is a very simple theory of relateeveety, which is why I'm using it more as a Minutiae Monday post rather on a Thursday where I started posting these theories.
Michael Hathaway in the 'Columbo' episode "Double Shock" could be the brother of Jane Hathaway of 'The Beverly Hillbillies'.
The danger in running these kinds of additions/alterations to long-running characters is that over time, there could be some dialogue that establishes a deeper background to the character than usually accepted in a thumbnail biography sketch.
For instance, the basics about Jane Hathaway is that she was a prim spinster with the hots for Jethro Bodine. She worked as the executive secretary of bank president Milburn Drysdale. Did she have a brother? Did she ever talk about her family? There's no mention of any family relations for Miss Hathaway in a wonderful book by Vincent Terrace - "Television Character and Story Facts".
Basically you just needed to know enough about a character to keep the plot humming from week to week.
As for Michael Hathaway, there was no need to know more about his character than it was shady. He was the lawyer for Clifford Paris and was willing to work with Clifford's nephews to keep control of the estate - even if he suspected strongly (and half rightfully) that one of them had killed their uncle. It wasn't exactly the situation to bog down the story with details about his family background.
So I think this is a safe theory to promote - Michael and Jane were siblings.
It could be that they were related to Walter Hathaway, a real estate agent whose "children" were three chimps, with his wife serving as the chimps' booking agent. And looking farther afield, somewhere deep in the Hathaway past was the common ancestor who would connect them to a British detective at Oxford, DS James Hathaway.
- 'Columbo' - "Double Shock"
- 'The Beverly Hillbillies'
- 'The Hathaways'
- 'Inspector Lewis'