Marvin, Samuel and Joseph were long gone from SC for twenty years before your Nancy Austell was born so she would have to be a descendant of William if she is connected to this family. The only information I have on this William came from the personal library of Ann A. Scott. She had him listed as William G. Austell, Sr.
William G. Austell, Sr. b: 26 May 1799 d: 26 Dec 1871 Burial: Austell Family Cem. near Gaffney, SC +Catherine Lipscomb b: 24 Jan 1812 d: 21 Jul 1895 in SC Burial: Austell Family Cem. near Gaffney, SC I don't have anything on their children but this looks like your best bet since they both died in SC