SARAH A. SMITH
Found her death certificate in the online database of MO State Archives:
States she was born: ca. 1851, died Nov-5-1930, buried Nov-7-1930 in Sligo, MO. Sligo is in Dent Co., MO just across the Crawford Co., line. The informant for this information was Edward C. Smith (I imagine the Clarence Edward in your post). I found no listing for Sarah in the Sligo Cemetery (Ozark Heritage; Dent County MO Area Cemeteries & Families Vol III 1994 by Ken Fiebelman).
I did find a Mary Effie Smith listing in Sligo Cemetery as the d/o William P. & Sarah A nee Walker Smith. Mary Effie died Sept 13, 1882, aged 11 yrs, 6 mos, 13 das. This could be a misprint with her age really being 1 yr, 6 mos, 13 das as she is not found on the 1880 census.
There was also a listing in Sligo Cemetery for a Young G. Smith (31-Oct-1805 - 15-July-1882).

I searched the cemeteries around Sligo, MO & found Sarah A. Smith in the Hutson-Walker Cemetery, Dent Co., MO as follows: 10-Dec-1851 - 5-Nov-1930. Further info was that she had lived in Hayti, MO for awhile. (See census info below).
I also found William P. Smith in the Hutson-Walker Cemetery as follows: s/o Young G. Smith, married Sarah A. Walker on 13-June-1875, 4 children: Edd, Florence, Leslie & Mary Effie E., no dates were given.

Sarah A Smith's death certificate lists her father as William Walker, again the informant was Edw. C. Smith, all other info, her father's place of birth, name of her mother & her mother's place of birth was unknown. The book by Ken Fiebelman lists Sarah's parents as Francis Marion "Frank" Walker & Elizabeth Roseann nee Short Walker. Frank was buried in the Sligo Cemetery, Elizabeth was buried in the Hutson-Walker Cemetery.

FLORENCE C. SMITH
Death Certificate lists her as Florence Spain.
Dates: 15-April-1878 Sligo, MO - 15-February-1947 St. Louis, MO. Buried: 15-February-1947, New St. Marcus Cemetery. Her father is listed as W. P. Smith born TN, her mother; Sarah Walker born IL. Informant was Bert Spain.

I found no listing for an Otto or Leslie Smith.

1850 Census lists Young G. & Wm. Smith living in District 1, Nichols, Cannon Co., TN.
1850 Census lists F. Walker (father of Sarah A.) in District 24, Crawford Co., MO in his father's household; D. Walker.
1860 Census lists Y.G. & W.P. Smith living in McCracken, Rutherford Co., TN.
1860 Census lists S.A. Walker living in Osage Township, Crawford Co., MO in her father's household; F.M. Walker.
1870 Census lists Y.G. & William Smith living in District 7, Davidson Co., TN.
1870 Census lists S.A. Walker living in Meramec Township, Dent Co., MO in her father's household; F.M. Walker.
1880 Census lists William P., Sarah A., Florrence C. & Yong G. Smith living in Osage Township, Crawford Co., MO.
1900 Census lists William P., Sarah A., Florence C., & Otto living in Randolph, St. Francois Co., MO.
1910 Census lists William P., Sarah A., Florence C. Spain & Clarence E. Smith in Hayti, Pemiscot County, MO.
1920 Census lists William P. & Sarah Smith & Florence C. Spain in Sainte Genevieve, Ste. Genevieve Co., MO
1930 Census lists Sarah E. & Clarence E. Smith as well as Florence C. Spain living in St. Louis City, St. Louis Co., MO.

Hope this helps.