Since you know when and where Roy and Grace died, you can obtain copies of their death certificates, which should show full names of their respective set of parents.With their complete names, they might be found on census records when Roy and Grace were children still at home.
You have slight typos in years for Grace in your post and you probably copied and pasted it, as your message history shows same dates.
CA Dth Idx:
Reynolds, Grace Cledious, b 20 Nov 1907 OK, d 13 Dec 1994 Kern Co, CA, 87 years of age.Mother Cooper and father Garrett.I'm assuming that's where you picked up surnames of her parents.
Since Roy diedmuch earlier, Grace was probably his informant, and she probably knew the names of his parents.Accuracy on death certificates only as good as the knowlege of the informant.Now, do you know who was the informant on Grace's DC?She shows up on the SSDI.You can always obtain a copy of the application she filled out herself when she obtained her Soc Sec card.It should show the names of her parents, her residence at the time of the application and other data, too.