I found two men named Dennis Danahy in Buffalo in that time period.
this is the one who died in 1904:
Dennis Danahy (c 1848, Ireland - 1904)
1875: age 30, fireman,
https://www.ancestry.com/search/collections/7250/records/1365717605 1880: age 36, keeps a boarding stable,
https://www.ancestry.com/search/collections/6742/records/38434206 1900: age 52, proprietor, livery stable,
https://www.ancestry.com/search/collections/7602/records/18731780 1904: survived by brothers John and Timothy, and a sister Mrs Bridget Coughlin
+ Ellen Mahoney
- Francis (c 1873 - )
- Dennis Danahy (c 1875 - )
- Edward Danahy (c 1877 - June 22, 1931, Detroit)
death record says parents Dennis Danahy and Ellen Mahoney, both born in Buffalo
- Gertrude Margaret Danahy (c 1879 - )
obituary
https://www.newspapers.com/newspage/363233670/-----
this is one who died in 1925
- Dennis Danahy (c Apr 1843, Ireland - 8 March 1925, Buffalo)
1892: age 48, butcher,
https://www.ancestry.com/search/collections/3212/records/683948 1900: b April 1843, foreman,
https://www.ancestry.com/search/collections/7602/records/32395198 1910: with the Reeses, foreman, packing company,
https://www.ancestry.com/search/collections/7884/records/17414174 1920: with the Reeses, foreman, meat company,
https://www.ancestry.com/search/collections/6061/records/86964995 findagrave:
https://www.findagrave.com/memorial/264026547/dennis-danahy findagrave says he was the brother of Michael and Matthew, the meat packers
+ Flora (c 1845, Ireland - ) on 1892 census but died before 1900
- Marie Danahy (June 1872 - )
+ Thomas J Reese (February 1873 - )
- Josie Danahy (c 1878, US - )
+ George Walter
- William Danahy (c 1872, US )
- Margaret Danahy (August 1883 - ) single in 1920
- Alice Danahy (November 1885 - ) single in 1920
You might need to look at the death records to sort them out for sure, hopefully.