I'm not sure if you've seen the family on census records.Ethel's father is Wm. J. McEwen on 1900 Stonewall Co, TX (all 7 living children are in the household); Jasper W. McEwen on 1910 Stonewall Co, TX (two children still at home), with Joseph E., Carl A. and Henry C. all married and living one after the other next door to their parents.
1910 census Borden Co, TX:
Sturdivant, William M., hd, 32, M(1) 8 yrs, b TX, MS, MS " Ethel L., w, 24, M(1) 8 yrs, 4 ch, 3 lvg, b TX, TN, MO " Jasper W., s, 7, b TX " Illa, d, 3, b TX " Ira M., s, 2/12, b TX Miller, William, boarder, 55, sgl, b TX
1880 census Brown Co, TX:
Category: Name;Relationship to head of household; Marital Status; Gender; Race; Age; Birthplace; Occupation; Father's Birthplace; Mother's Birthplace.
W.L. STURDEVANTSelfMMaleW31MSFarmerALAL P.C. STUDEVANTWifeMFemaleW32MSKeeping House------ Ida G. STUDEVANTDauSFemaleW6TX------ I.L. STURDEVANTSonSMaleW6TX------ J>t. STURDEVANTSonSMaleW5TX------ M.W. STURDEVANTSonSMaleW3TX------ L.M. STURDEVANTDauSFemaleW1TX------ M.W. could be William M. with names swapped as you can see what happened to Ethel's father.And, the parents in this household are both born in MS, MS, as shown for William on 1910 census.
If these were my lines, I would check land and probate records in the counties where these families are located, see if you can find heirs for W.L. Sturdivant, does your William show up?