1900, Brooklyn, 153 Wilson Street
Boyd, John, born Jun 1822, married for 38 years, born Ireland, parents born Ireland, immigrated 1860, naturalized, occupation - porter, owned the house free of a mortgage, can read, write, and speak English
Boyd, Fannie, wife, born Jul 1824, married for 38 years, mother of 3 children, 1 living, born Ireland, parents born Ireland, immigrated 1860, no occupation, can read, write, and speak English
Boyd, James, son, born Dec 1865, married for 3 years, born New York, salesman, can read, write, and speak English
Boyd, Mary, daughter-in-law, born Oct 1865, married for 3 years, no children, born New York, parents born New York, no occupation, can read, write, and speak English
Boyd, Ada, granddaughter, born Aug 1899 in New York, parents born New York, attended school for 9 months, can read, write, and speak English
Stevens, Annie, granddaughter, born May 1881, single, born New York, parents born New York, occupation - clerk
Fannie and Nancy are nicknames for Ann, as far as I know, so I wouldn't rule her out on that. With an Annie in the house, they might have been trying to distinguish between the two.
If they were right on daughter-in-law Mary having no children, maybe Ada belongs to someone else?