I started from the beginning and you've probably already have this info but just in case you don't, I've included it.
An Oscar A. Stewart on Sept. 12, 1918 was living in Cullman, Cullman Co., Alabama.
Born=23 July 1885.
Nearest Relative=Emma Stewart, wife, same address as above.
Source=World War I Draft Registration Cards 1917-18.
In 1920 they were living in Civil District 5, Lawrence Co., Tennessee.
Oscar A. Stewart, b. AL, 33, general farmer.
Emma J., wife, b. AL, 31.
Nettie Lee, b. AL, 11.
Gladis R., b. AL, 9.
Iva L., b. AL, 9
Ruba [Ruby] E., b. AL, 3 corrected to 3 2/12ths.
Ernie V., b. AL, 6/12ths. [died young?]
In 1930 they were living in Seattle, King Co., WA.
Oscar A. Stewart, b. AL, 50, marr @ 29, laborer flour mill.
Emma, wife, b. AL, 42, marr @ 19.
Iva, b. AL, 16.
Ruby, b. AL, 13.
Billy, b. AL, 10.
Marjorie, b. TN, 7.
Pauline, b. TN, 5.
Archie Mcclard, uncle, b. Can-Engl, 52, widower, immigrated 1889, naturalized, teamster electric co.
It is much more difficult to find info after the 1930 Census because that's the latest one available to the public at this time.
An Oscar Alfonza Stewart
Born=23 July 1885, Alabama
Residence=9450-15th SW, Seattle, WA
Occupation=H. C. Wehisly, Fisher Flour Mill, Harbor Island, Seattle.
Source=U.S. World War II Draft Registration Cards 1942.
An Oscar A. Stewart
Died=23 March 1950, Grant Co., WA per death cert #4009.
Source=Washington Death Index 1940-96.
You can find his obituary at the Washington State Library, sos.wa.gov/library/obituaries.aspx.
Also after 1930 about the only info you'll find is the death info, however, obituaries can be a great source and provide clues about where the children were living in later years.
A Jack Edward Hall married Iva L. Stewart Sept. 6, 1930 in King Co. Source=Washington Digital Archives, digitalarchives.wa.gov/.
You find more details at this website.
An Iva L. Hall
Born=12 Nov 1915
Last Residence=Garden Grove, orange Co., CA
Died=21 Aug 2003.
Her social security # was assigned in WA before 1951.
Source=Social Security Death Index.
There's no guarantee she's your Iva. You can find her obituary or death certificate to verify that she is.
Go to obitsarchive.com and look for Orange County Register. They charge a fee but it's nominal.
contact the Orange County Clerk-Recorder, egov.ocgov.com/ocgov/Clerk-Recorder and purchase a copy of her death certificate.
A George W. Elwell married Ruby E. Stewart March 2, 1935 in King co., WA. Source=Washington Digital Archives, digitalarchives.wa.gov/ .
A Ruby E. Elwell
Born=Nov. 24, 1916
Died=Aug. 8, 1996, Seattle, King co.
Source=Washington Digital Archives, Social Security Death Index, digitalarchives.wa.gov/
You will find an obituary volunteer at raogk.org, read guidelines, Click on K, scroll down to King County and choose one volunteer.
I didn't find William Stewart's marriage or death info and I looked through Washington Digital Archives and FamilySearch. Hopefully there will be clues about where he was living in the other's obits.
A Marjorie C. jacobson
Born=2 April 1927
Last Residence=King Co., WA 98028
Died= 26 May 2003.
Her soc. sec. # was assigned in North Dakota.
Source=Social Security Death Index, familysearch.org/.
Unfortunately I didn't find anything for Pauline. Successful Searching!