Scroll down to about the bottom third of the page.It mentions that in addition to his wife and children he is survived by two brothers, Eugene V. and Robert F.
I found this family in Washington, D.C. in 1930: KNOTT, James H. age 40 b. MD, both parents b. MD wife Lucy B. age 39 b. VA, both parents b. VA son Randolph H. age 16 b. DC son James H. age 13 b. VA son Eugene V. age 11 b. MD son Robert F. age 6 b. MD
In the 1940 census Richard states he was born in DC.
I can't find them in the 1920 census.
There's a possible match for James' family in 1900, Pomonkey, Charles, MD: KNOTT, Richard b. Nov 1848 in MD, married 18 yrs, both parents b. MD wife Emma E. b. Sept 1865 in MD, 9 children born, 5 children living, both parents b. MD son Thomas E. b. Aug 1883 in MD dau Margaret R. b. Dec 1887 in MD son James H. b. June 1889 in MD dau Ceclia G. b. Jan 1898 in MD
I think Emma might have been his second wife.In 1880 in the same location there's a 30 yr old Richard KNOTT, widowed, living in the household of George and Kansas HUNTT.
There's a christening record for a Richard Thomas KNOTT, b. 9-Nov-1848, christened at Roman Catholic, Mattawoman, Charles, MD in June 1860.Mother's name Maria Louisa KNOTT.Father not listed.
1860 census for Bryantown, Charles, MD: KNOTT, Maria age 29 b. VA Charles age 18 b. MD Richard age 11 b. MD Sarah age 9 b. MD Marry age 6 b. MD John age 3 b. MD