Joyce, I don't have anything on Horace but I do have some different info for the rest of the family, which may or may not help. I'm guessing that it may, so here goes.
Ada M. Gifford b. November 1862 probably in Holliston, Mass. Her mother Celia was living with her in 1900, still in Holliston, she was born Jan. 1838.
According to F.C. Pierce Ada was actually married to Walter Henry Fiske not Lewis W. Fisk. Lewis Worthington Fiske was her oldest son and he was born April 6, 1887. Her other children were Marion Alice Fiske, b. Oct. 26, 1888 and finally Walter Raymond Fiske b. Oct. 15, 1890, all were born in Holliston Mass.
Walter Henry Fiske was born April 27, 1864 in Holliston and he was the son of Milton Fiske and Ellen Sophia Worthington.
How sure are you of her being married to Lewis W. because Pierce has been known to make mistakes but the dates seem to fit his version fairly well.