The Beverly Hillbillies premiered in 1962 and told the story of Jed Clampett and his family. Up next was Petticoat Junction, which premiered in 1963. It was a sitcom about a hotel known as The Shady Rest, which sat next to the local train depot. Green Acres, which was the final show in the trilogy, premiered in 1965 and was the mirror opposite of The Beverly Hillbillies. See www.poobala.com/hooterville.html for more details.
I believe some of tbe characters in each show were relatives or friends of chracters in others. Several of the actors played parts in the other shows. The main female lead in PJ also played Jethro's mother in BH.