Texas mandated vital records (birth and death) effective 1903. Compliance with the law was haphazard for several decades thereafter. There were very few birth certificates filed 1903-1930. Occasionally, daily research uncovers someone who died and was buried in 1950s with no certificate. Alrighty then, Richard Walker and Mary Lou (nee: Harwell) had three children that were born in Giles County, TN and died in Texas. The siblings were: Walter E. Walker (12 Mar 1868 - 21 Jun 1947), Ada Ann (nee: Walker) Hickman (16 Apr 1870 - 19 May 1957), and Charley Edgar Walker (27 Sep 1872 - 7 Jan 1958). You husband descends from Charley and his wife Nudie (nee: Harris) Walker (27 Jun 1875 - 7 Jan 1964). All of those lifespans found on death records viewable/printable https://familysearch.org/
"Nudie" taken from death certificate but the name has a variety of spellings on census records: Newdie, Neudia, Neudie, Nudia, etc. C. E. Walker wed "Newtie" Harris 15 Nov 1891 in Ellis County, TX. Start in 1870 TN-Giles-District 10-Image 6 and search for R. M. Walker age 36. Next, 1880 TN-Giles-District 10-108-Image 8 look for Richard Walker age 46. Guessing Richard Walker died prior to 1896 'cause his widow remarried to George W. Martin in Ellis County. The Walkers settled primarily in Forreston, Ellis County and many are buried there together with members of the Harwell family.