I believe I've found a fourth child, Henrietta, of Millis MITCHELL Sr. He was born about 1845 in South Carolina, arrived as a slave in Sugar Land, Texas betweeen 1856-60, moved to Houston, Texas about 1880-82. His two known wives are Emily WILLIAMS and Henrietta EDEN. His known Texas-born sons are Jack (b. 1869), William H. or William A. (b. 1877), and Millis E. (b. 1879).

1900 census, Houston, Harris County, Texas:

Household head
MITCHELL, Henrietta S., 42 (b. 1858), married 25 years, mother of six living children of six born, wash woman, b. in TX, father b. in FL, mother b. in TX

Daughter
MITCHELL, Henrietta, 13, single, no occupation, b. in TX, father b. in SC, mother b. in TX

Also in 1900 census, Henrietta MITCHELL, wash woman, is counted as the widowed mother of household head William (Wm. A.) MITCHELL and his brother Millis MITCHELL. They lived on Buckner St. in Houston.

Marriages in Fort Bend County, Texas:

MITCHELL, Miles (Millis?) and EDEN, Henrietta filed 15 Feb 1875 (#00009975)

MITCHELL, Millis and WILLIAMS, Emily m. 27 October 1868 (#00080169)