Let me see what I can find in this Brown County cemetery list, compiled abt.1998 by H. Lyle Hinz of the Brown County Genealogical Society. I'll just post what I find listed & let you sort out the details. (good luck)
In the Morrill Cemetery, Morrill Township, Brown Co.
COOK, Infant, b.1885, d.1885, "child of S.& E.M."

One individual buried in the Laus Creek Cemetery (also known as the Anderson Cemetery), in Padonia Township, Brown County, Ks.
COOK, Sister Malinda, (no b. date), d. 22 OCT 1894, "mar: Ira 4 JUL 1886, aged 25y 8m 21d, died at Rulo, Nebr."

I see 11 individuals buried in the Horton Cemetery under the name COOK, but none with any of the 1st names you mentioned.

Then in the Richardson County, Neb. cemetery list book, Vol. 4 (compiled by the Tri-State Corners Genealogical Society abt. 1996);
buried in the Rulo Cemetery in Rulo Township under COOK:
Cecil b.1904 - d.3/9/1962
Florence b.1912 - d.4/2/1950
Harry Edwin b.7/9/1902 - d.2/1/1993 (married 2/13/24 to Hattie Ellen Cook)
Harry (no stone) died 5/23/1977
Hattie Ellen b.5/1/1907 - 10/28/1988 (wife of Harry Edwin)
Lulu b.1898 - d.1969
William S. b.2/4/1892 - d.4/12/1972 "MO Pvt 38 Inf WWI"


Keith