We have a John Worth Carnahan who fits the time frame, the geographic location and a brother named Charles Carnahan.
Here are the details followed by those of his brother Charles (and other siblings) and of his father (William H. Carnahan) and a bit on his Grandfather and G Grandfather:
John Worth CARNAHAN (11/12/1865 - 07/16/1946) married Mable N. ---------- (abt. 1873 or 1874 - ?). John was born in PA and died in Los Angeles, CA. Mable was born in Illinois. In 1880 John was living in Burrel Twp., Armstrong Co., PA. In 1913 he was living in Washington, DC., and in 1920 both he and Mable were living in Washington, DC. In 1934 he was living in Chicago, Cook Co., Illiinois. Together, John and Mable had four children: 1) Worth CARNAHAN (01/31/1896 - 06/__/1973) born in Illinois and died (probably) in Davidson Co., TN. In 1920 he was living in Washington, DC. 2) Mayna(rd?) CARNAHAN (abt. 1899 - 1900, died - ?) Mayna(rd?) was born in Illinois. 3) May Worth CARNAHAN (abt. 1905 -1906, died -?) was born in Washington, DC, and was living there in 1920. 4) Audra Bell CARNAHAN (abt. 1911 -1912, died - ?) was living in Washington DC in 1920.
John Worth Carnahan had a brother named Charles Carnahan who fits the description of the brother named in the Washington Post articles:
Charles CARNAHAN (abt. 1867 - 1868 - died - ?) was born in PA. In 1880 he was living in Burrell Twp, Armstrong Co., PA and in 1913 he was living in Chicago, Cook Co., Illinois.
John Worth and Charles were the 2nd and 3rd of a total of 12 children in the family. The others were:
1) Hallie Carnahan; 4) Clara May Carnahan; 5) Cora D. Carnahan; 6) Harry H. Carnahan 7) Homer I. Carnahan; 8) Flora J. Carnahan; 9) Myrtle Carnahan; 10) Grover C. Carnahan; 11) Wells Vernon Carnahan; and 12) Ralph Norman Carnahan.
John Worth's father was William H. Carnahan: (09/30/1839 - 07/04/1914) married Maria Louisa McKee (10/10/1844 - 12/10/1934) William was born in Allegheny Co., PA and died in Apollo, Armstrong Co, PA. Maria was born in Pennsylvania and died in Chicago, Cook Co., Illinois. In 1880 they lived in Burrell Twp, Armstrong Co., PA. In 1900 and in 1910 they lived in Apollo, Armstrong Co, PA. In 1920, Maria lived in East Conemaugh, Cambria Co., PA. Both William and Maria are buried at the Apollo/Riverview Cemetary, Armstrong Co., PA. Together they had 12 Children.
Continuing back in their lineage - William H Carnahan's father was John CARNAHAN (Abt 1795 - 09/23/1883) who married Mary Funk (03/01/1810 - 08/12/1876). John was born in Allegheny Co., PA and died in Apollo, Armstrong Co., PA. He was buried at the Dunkard Church Cem., Burrell Twp, Armstrong Co., PA. In 1860 he and Mary were living in Kittanning, Armstrong Co., PA and in 1870 they were living in Cochran Mills, Burrell Twp., Armstrong Co., PA. Together John and Mary had 8 children although an infant son was never named.
This John Carnahan's father was William Carnahan (born ? - died before 12/26/1815) who married Nancy (maiden name either Dawson or Henrie). Both William and Nancy were born in Ireland. William died in Pittsburgh, Allegheny Co, PA. Of their five children, two were over fourteen when William died. At the time of the settlement of William's estate (12/26/1815 - Allegheny County, PA Court Records), the youngest three children, (Henry, James and Jane Carnahan, who were all under the age of 14), were put under the guardianship of Ralph Dawson. At the time of the settlement, Nancy Carnahan had re-married to a James Anderson (or Andersen). Interestingly, a few years later it is noted in the Westmoreland County, PA probate records that a John Frederick of Washington Township, Westmoreland Co. PA was appointed guardian of the same three children in 1818. (Probate Ref: 1OC173N1818 Page 282, Volume 1, "Estate of William Carnahan administered by James Andersen and Nancy Carnahan Andersen - 12/26/1818"). Nancy later married for a third time to a Mr. Proudlock
It all looks like a fit to me.