First here's the info on John Knox.
In 1880 he was living in Columbia Co., WA.
John Knox, b. IL, 20, teamster, single.
In 1889 he was living in Columbia Co.
J. R. Knox, b. IL, abt. 1860, barber.
M. F., wife, b. IL, 24.
Melvin, b. KS, 6.
In 1890 according to the Veterans Schedule he was living in Columbia Co.
In 1900 he was still there.
John M. Knox, head household, b. IL, Oct 1859, divorced, barber.
On 25 December 1901 in Walla Walla, Walla Walla Co., WA
a John R. Knox of Columbia Co. married
a Alice L. Gibson of Columbia Co.
Source=Washington Digital Archives, media.digitalarchives.wa.gov/ . You can view and print this document at no charge at this web site.
In 1910 in Dayton Ward 2, Columbia Co
John R. Knox, b. IL, 50, divorced, barber.
A John R. Knox
Number of Marriage=4th
Father=John P. Knox, b. NY
Mother=Olive Tripp, b. ME
married9 Oct. 1913 in Walla Walla, Walla Walla Co a
Age=23, b. Oregon
Number of Marriages=2nd
Father=John Sluman, b. Canada
Mother=Jennett Kerr, b. Ontario, Canada
Source=Washington Digital Archives, media.digitalarchives.wa.gov/ .
A John R. Knox
Died=13 Jan 1922, Dayton, Columbia, WA
Father=John P. Knox
Source=Washington Digital ARchives, digitalarchives.wa.gov/ .
If you're interested in his obituary, contact the Washington State Library, sos.wa.gov/library/obituaries.aspx . There is no charge and it takes about four weeks.
Then I found this information about Edith and Melvin.
In 1900 A Katherine E.Knox and children were living in Brookly, Columbia Co., WA.
Katherine E. Knox, b. Russia, April 1862, widow [sometimes women said they were widowed instead of divorced because of the divorce stigma].
Byron Chamberlain, son, b. KS April 1881, day laborer.
Frank Chamberlain, son, b. KS, April 1882.
Edith R. Knox, dau, b. WA, March 1894.
In 1920 Melvin and Edithwere living with their grandfather in Dayton.
John P. Knox, b. NY, 75, M1=55 yrs, no occupation.
Melvin Knox, grandson, divorced, b. KS, 28, can't read occupation but both parents born IL.
Edith Knox, granddau, b. WA, 16, father born=IL and mother born=Russia.
I think Melvin's mother was the M. F. Knox on the 1889 Census and Edith's mother was Katherine E. Knox found on the 1900 Census. Successful Searching!