I've been researching this recently for a close friend, who knew your grandfathers sister. Census records report your grandfather as Ossie or Osa born in Kentucky around 1884. Census records also report your grandmother name is Hazel P Gragg born around 1897 in Kansas. It does not show her maiden name.

Census records also report your dad had five siblings Gemima 1915; Fern 1916; Arizona 1920; William (Billy) 1923,
Letha 1926 and Oleva Jean 1929.

Gemima and Fern was born in Kansas. Your dad and uncle Billy was born in Texas and Aunt Letha and Oleva was born in Oklahoma.

Census records also reflect that by 1940 your grandmother and Grandfather was divorced and that your grandmother, ncle Billy Aunts Letha and Oleva was living at 210 S Frankfort street Tulsa Oklahoma