I found something that may be of interest to you. I ran across a google book that has information about a Charles M. Tunstall (1854-1933) who married Emma Mason (1855-1939). This Tunstall family lives in precisely the correct spot. The book even mentions the old family home "Alabama", a name I recognize as the home of our Tunstalls through family accounts. It lists the children of Charles and Emma as Richard Evan Tunstall, Mrs. Stanley Gardner, Mrs. Thom. E. Warriner, and James T. Tunstall of Quinton, Virginia.
What is curious to me is the initial in Charles' name. Are you sure the tombstone you found with Emma's said Charles C. Tunstall? If so, I'll write the M off as a typo and know that these are my Tunstalls. Thank you.
Old New Kent County [Virginia]: Some Account of the Planters ..., Volume 1 By MALCOLM HART HARRIS, MD