I would love to know what you have found. I believe they are his siblings in 1880. Since I posted the above, I found the following death notice for Gilbert in California.
California, Death Index, 1940-1997
Name: Gilbert Materson Gay
Event: Death
Event Date: 06 Feb 1956
Event Place: Kern, California, United States
Birth Date: 20 Mar 1875
Birthplace: Alabama
Gender: Male
Father: Gay
Mother: Allen
Jennifer
California, Death Index, 1940-1997
Name: Gilbert Materson Gay
Event: Death
Event Date: 06 Feb 1956
Event Place: Kern, California, United States
Birth Date: 20 Mar 1875
Birthplace: Alabama
Gender: Male
Father: Gay
Mother: Allen
Jennifer