I don't have a lot of info on any of the Selfs. Sarah Langley supposedly was the daughter of Rachel Self McAbee's sister, according to my uncle. Sarah married Thomas Simpson. My mother and her siblings all remember "Aunt Sary" and "Uncle Tom." I've found them listed in the Arkansas census, I forget the year, but it lists Sarah's birth year as approx. 1874 as I recall. I found a Sarah Langley born that year in the 1880 census for Oak Bluff, Clay County Arkansas. It lists her as living with her mother, Mary Langley, a widow, age 35, who was born in TN. Sarah's father was born in Arkansas according to the census and so was she. Also a Fransis Brownen, age 12, listed as "other" not a relative is living in the same household. I haven't been able to tie this Sarah clearly to my Sarah Langley Simpson though, except by circumstantial dates.
One interesting thing though - two household down from Mary Langley's is a William Glasgow, age 25, wife Sarah, age 34, and stepson James Williams, age 13. Tantalizing, since family tradition said Rachel had a sister married to a Glasgow. Sarah Glasgow was also born in TN like Mary Langley. Could this Sarah be Mary's sister and thus Rachel's sister? Also, tantalizing, Robert F. McAbee's mother's maiden name was Williams. Could these people be related on that side, rather than on Rachel's, despite family oral history to the contrary?
Then, several households up from Mary Langley's, we find William Lell, born TN, his wife, Nancy, born MS, and Fransis Self, Perry Self, and Rachell Self - listed as his niece in law, nephew in law, and sister in law respectively. This Rachell, born in AR as was my Rachel, is listed as 28, which would make her too old to be my Rachel, UNLESS there was a mistake in the census date or transcription which is perfectly possible. My Rachel supposedly had a nephew Perry Self, but this Rachel looks like she's married to a Self, NOT a Self, and that these are her kids. Could the elderly relatives have been wrong about her maiden name? Possible...maybe she was a Self by marriage instead of by birth. I know from marriage records that she was a widow before she married Robert Franklin McAbee. Who knows. Sigh. Wish I could figure this all out.
Maybe you'll have better luck than I have. You might want to follow up on James and Sarah Glasgow if they look to be the right age to be the parents of William Thurston. The names sure look right.