You might check the Bowie Co, TX GenWeb site, some GenWeb counties are putting their cemeteries online, and you might find Yancy and Charles buried there, maybe even other family members, too. Archibald might have lived out his "golden" years with one of his sons, and ended up dying there, too. If you can find death dates for Yancy and Charles, look for obituaries. You never know what info might pop up in an obit. Survivors are often listed, and if they live out of the area, they sometimes state where the survivors reside. You might pick up some of the other brothers(?)
Also, post your query on that site, plus ask if anyone has a county history, and would they check for any possible information on this Williams family.