You're right, David- Jed's wife was the late Rose Ellen Moses Clampett. Elly May's full name (according to a later color episode) is Elly May Margaret Clampett. Jed and Pearl (Jethro's mom) were first cousins, but Jethro called him "uncle".
I assume you mean Jim Pierson- he's done a lot of the MPI stuff, from Dark Shadows to The Doris Day Show and beyond. And he's a nice guy too boot (I've known him for years!).