Determining the maiden name of Virgie's and Lizzie's mother requires detective work, but the process is straightforward. The informant was Lizzie Scarbrough on the Missouri death certificate of Joseph Carroll Burton (#4285-a, 10 January 1919). This was surely the same man who was living with Lizzie and Will as "servant" on the census in 1910. Investigating further shows that the 1870 US census in Scott County, Missouri, page 17, reverse page of stamped 545, lists Joseph Burton, 20, born in Tennessee, Anna Burton, 17, born in Missouri, and Felix Denton, 19, born in Missouri. Joseph and Anna had been married less than a year having married in August (apparently August 1869). In 1860, on the census, Felix Denton, 9, and Ann Denton, 8, were in the family of Eliga Denton in Scott County on page 63.
Lizzie and Will had no children. She probably married Will in order to care for and raise deceased Virgie's infant Jack and almost infant John.
William was married to Wanda Nelson, and they had two sons
John Marshall was married to Shelby Sitz, and they were parents to three daughters.
I have almost no data on the marriage of Fanny Lee and William. Although I corresponded with Fanny's niece, who gave my some information, I have misplaced all my notes from then.
According to his obituary, William came from Tennesse to Scott County with Jeff and Alice when he was 14, which would have been around 1888. The obituary says that his surviving children were sons Jack (Andrew Jackson), Bill (William Jr), and John M., and daughter Bessie Alice. Also surviving Will were half-brothers Arthur Smith, James Smith, Bob (Robert) Smith, and Albert, and two unnamed grandsons.
Family Search data online (familysearch.org), Scott County Marriage Book, page 260
1900 Census, Scott County, Missouri, sheet 7, 109 B stamped: Lee Scarbrough, August 1876 TN TN TN, May, December 1880, KY TN KY, Frank, son, May 1890, W. A., bro, December 1874, TN TN TN
1910 Census Scott County, Missouri, page 215A: W. A. Scarbrough, 36, m1 3 y, TN TN TN, Elisbeth, 39, IL TN MO, m1 3 y, 3 ch / 3 liv, Bess 6, Andrew 3, Elbert Myers, 20, stepson, MO KY IL, J. C.(?) Burton, 64, servant, TN NC TN, Bertie McFall, 14, servant, MO Un MO, Charlie Smith, 26, boarder, TN TN TN
Charles Smith was half-brother to William, and J. C. Burton was probably Elizabeth's father. I don't know why they were not identified. Both Will and Lizzie were in second marriages instead of first as stated here.
1920 Census, Scott County, Missouri, page 5B 208B stamped: Wm. Scarbrough, 46, TN TN TN, Lizzie, 49, wife, MO TN MO, Bessie, 16, dau, MO, Jack, 13, son, MO, Elbert Myers, 26, nephew, 26, neph, MO KY MO, Roy Hesinger, 32, hired man, MO MO MO
All other sources including later censuses support Elbert's being 30 at this time. He was also Will's stepson, not his nephew.
1930 Census, Scott County, Missouri, 23page 2A: William and new wife Fanny Lee and son, 6, who may still be alive. Jack also lived there. Alice was living with William as widowed mother,
1880 Census, Scott County, Missouri, page 2 267 B stamped: Joseph Bourton, 32, TN TN TN, Jennnie, 34, wife, MO MO MO, Elizabeth, 10, dau, IL TN MO, Verjinnie, 5, dau, IL TN MO, Addie Burnes, 7, step-dau, MO MO MO, William Denton, 24, laborer, MO TN TN, Samuel Hamilton, 22, laborer, MO MO MO
Note: William Denton06 A stamped: Lizzie Myers, born November 1870, wid, 2 ch / 1 liv, IL TN MO, Elbert Myers, son, born October 1889, MO KY IL, Virgie Burton, sister, born January 1875, was probably the brother of Joseph's deceased first wife Anna Denton, the mother of Elizabeth and Virginia.
1900 Census, Scott County, Missouri, sheet 4, 1 MO TN MO, John Scarbrough, born December 1878, boarder, TN TN TN, Chas. Smith, born May 1882, TN TN TN
Note: Lizzie was born before her family came to Missouri, and Virgie was born after the move. Charles Smith was half-brother to John Scarbrough and Will Scarbrough.