The city directories list another Vaughn family living near Margaret and Dennis at 2109 Penn. The head of this family is Michael Vaughn, co-proprietor of the saloon with Dennis. Listed at the same address as Michael are a Michael Jr. and Edward. J., who are shown to be Michael's sons by the 1900 census. In 1904, Michael S. is a bartender and Michael J. is a laborer with the water department.
The 1904-1918 city directories show a Michael and Margaret Vaughn from 1904 through 1918 at 2109 Pennsylvania Avenue. The occupation of Margaret was listed as a saleswoman at Emery Bird Thayer Dry Goods Company in some later years. Michael was a foreman for the Street Cleaning Department. The same Michael (foreman for the city street dept.) was still living at that address in 1920 in the census\footnote{Jackson Co. ed. 43 page 8}. From the census, Michael also had a wife named Margaret (born August 1858 in Illinois) and a daughter Margaret. Michael's daughter Margaret is the saleswoman in the city directories since she has that same occupation in the 1910 census.\footnote{Jackson Co. ed. 42, page 1A} Thus, the Margaret in the 1905-1918 directories is not Margaret Shannon Vaughn.
Michael Vaughn was born in September of 1849 according to the 1900 census.\footnote{ Jackson Co., MO, ed. 43, page 1A} He immigrated in either 1869 or 1871 according to the 1900 and 1920 censuses, respectively. This fits well with a statement in Dennis Vaughn's obituary that Dennis had been in Kansas City for 30 years. In 1900 the same Michael listed his occupation as Saloon keeper and his son Edward J. was a bartender. Children of Michael and Margaret included Michael (b. 1875), Edward (b. 1881), Lilian (b. 1885), Teresa (b. 1890), and Margaret (b. about 1894, maybe named Loretta in the 1900 census).
I don't mean to go into such detail about Margaret's in-laws, but it seems important to also know which possibilities are eliminated. From his age, Michael does appear to be a brother to Dennis, not a father or son. But we're still left with the question of what happened to Margaret and her son Andrew after about 1904. Apparently they either moved or both died.
Sources for this individual: @S890@ @S700@ @S891@
