Since your father was born in Henryetta, Okmulgee Co, OK, do you know if his parents stayed in that county?If so, check the Okmulgee Co, OK GenWeb site, some GenWeb counties are putting their cemeteries online.If not on the county site, check the archived section of the OK GenWeb Project for additional county records.If you can determine when and where they died, you can obtain copies of their death certificates, which should show the names of their respective set of parents.
Also, if you can learn their date of death, look for obituaries, you never know what helpful tidbis may turn up in obits.Survivors are usually listed, and if they lived out of the immediate area town/state of their residence might be included.A good way to pick up names of any female family members, too.
Also, post your query on that county GenWeb site, too.
Have you found Charles and Miranda on the 1900 census?Or, any census record?How reliable is your source for birth years and state of birth for Charles and Miranda?Keep in mind "IA" at one time stood for Indiana, so sometimes itcauses confusion over whether state should be Iowa or Indiana.Like we don't have enough problems, right? (^_^)
Here is a "possible" match for your uncle Homer from SSDI:
Homer Hamer, b 4 Jan 1895; d Jan 1964; last residence OK; SS card issued in OK.
I see from CA Dth Idx your father died in Marin Co, CA, did any other family members go to CA?