The coincidence here is the visual similarity between my great-grandparents and Ma and Pa Kettle. 

My great-grandparents were farmers in Skagit Valley, WA.

Ma and Pa Kettle had 15 children. My great-grandfather came from a family of  at least 11 children. 

While not from the Ozarks of Arkansas, my great-grandparents were originally from Kansas.

Now there were families who believed or claimed the stories were about them.

One of these was the Bishop Family. They even took Betty MacDonald and the Bone Marche to court, but the judge ruled against them.