They were married on 12-23-1794 at Wilson Presbyterian Church, Old Stone, Augusta County, Virginia.
William served as 2nd Lieutenant of a Virginia Calvary Troop commanded by Capt. Robert Gratton, then as a Lieutenant in the 3rd Division sent to Pittsburg.
Facts about this person:
Mg.Sur: John McDowell
The Family Bible lists the following children born to William and Elizabeth:
Alexander M (died in infancy)
Sally (died in infancy)
Betsy, who married Bird S. Grils in 1820
Mary Jane, who married a Kingsolving
William Augustine, who married Virginia L. Kingsolving in 1830 and had 8 children. He built the house "Solitude" in 1832.
John K. (died in infancy)
Isabella, who married Charles L. Grills and was the mother of Byrd S. Grils
Shelton Spillsbury, who married Martha Jane Davis. Their daughter Minnie married Byrd S. Grils.
In William's will from 1828, a daughter Ann is named and Nancy is not named, although she was alive until 1879. In the 1860 census, Nancy is listed as Ann, so it is likely that this is the same person.
William served as 2nd Lieutenant of a Virginia Calvary Troop commanded by Capt. Robert Gratton, then as a Lieutenant in the 3rd Division sent to Pittsburg. 
The following people were named in William's will:
Sucky, a woman, (bequeathed to his wife Elizabeth and at her death to be sold and the proceeds divided equally among his legatees)
Benjamin (the younger), a boy, (bequeathed to his son William)
Harry, a boy, (bequeathed to his daughter Ann)
Ezekial, a boy, "now in possession of Bird S. Grils" (bequeathed to his daughter Lettitia)
Jane, a girl, "now in possession of Jefferson B. Kingsolving (bequeathed to his daughter Isabella)
Alexander, a boy, "now in possession of Edward Mulholland" (bequeathed to his son Shelton)
Joshua (bequeathed to his son Lycurgus)
James, a boy
John, a boy
More "servants" are mentioned but not named, "to be distributed among my legatees at the death of my wife if not thought most advisable by my executors to dispose of them previous to that for the benefit of the estate".
William is buried at Tinkling Spring Presbyterian Church Cemetery, Fishersville, Augusta County, Virginia.
WikiTree profile Abney-147 was created through the import of McClanahan-20121014.ged on Oct 15, 2012 by Anonymous McClanahan.
Will of William Abney, dated June 16 1828. Will Book 16, Page 363, Augusta County, August 25 1828. Transcribed in Abney Metzger, C. A. 1978 "In search of Kate, Abney, Geisinger, Davis, Parks, McClanahan, Shelton, Van Lear families" 
It may be possible to confirm family relationships with William by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree:
Abney-762 and Abney-147 appear to represent the same person because: Abney-762 and Abney-147 were both married to Elizabeth McClanahan, daughter of Col. Alexander McClanahan, and are thus the same person.