This doesn't address the Austentine Hazeltine part of the mystery very well but I think I know who Joel Ann was.
In 1850, William Powell age 18 is living with his parents on page 254 of the Laurens County census.In 1860, he is living with Joelann H Powell age 17—presumably his wife.
Searching the 1850 census in Laurens County for any Joels, I only found one female—age 8 who was Joel Ann Sanders, in the household of Coleman Sanders age 57 and his wife Emily age 37 (on page 269.)There were other children whose names were difficult to read.
I also found at Ancestry, a marriage record for Darsey, Emily Sanders, Coleman 21 Mar 1844 Georgia Laurens County
Since Joel Ann, would have been born prior to the 1844 wedding date, it would appear that she was Emily’s daughter but not Coleman Sander’s.Whether she was an illegitimate daughter who was given her mother’s maiden name or whether her mother was the widow of a desceased Dorsey is a question for further research. She apparently took her stepfather's name when he married her mother.Perhaps he was really her father. Maybe her mother gave her a fanciful name of Austentine and then changed it to Joel Ann when the girl's father died.(Wild speculation:) It's reasonable, I think, to guess the H. in Joelann Powell's name could be for Hazeltine.
In my rather cursory search, I didn't find any record of Joel Ann in 1870.