I think that there may be a possibility that your grandfather is related to me.My grandmother has several people in her family tree named Joseph Prenosil.John and Frank also seem to be common names for the family, which wasn't very creative with naming.Here are some of the relatives:
Joseph Frank Prenosil I (born in Czech, married to Anna Semerad, both moved to Nebraska)
Their kids: Anton, Frank, Joseph Frank Prenosil II, Anna, Katie, Mary, and John.At least some of them lived in Nebraska.
Joseph Frank Prenosil II married Amelia Shorney and had 6 kids.One of those children grew up to be my grandmother's mother.
With the many Joseph Prenosils, the Johns, and the repeated middle name of Frank in my family, your relatives seem to fit the pattern.Plus my ancestors had strong ties to Nebraska and most stayed in the mid-west.My grandmother has more info that I could send you.