I've been doing a little research and found a lot of similar data and some inconsistent ones. Seems they had left out the fact there was one child born to Henry and I found 3 name variations used for Phoebe:

Phoebe Ann (Being the one with Demarest birth records)
Phoebe Mariah (none listed in Demarest genealogy)
Phoebe Julia (none listed in Demarest genealogy)

Phoebe could have started using her baptizmal name instead of Ann, I don't have a good explanation for that. I have found some consistent marriage dates for Ann and Mariah, both records I found show the marriage for 7 Jan 1830 at United Presbyterian Church Of Broadalbin, Perth, Fulton, New York. But, all of them only show one child, James Bont Kested.

James Bont Kested
Born: December 11, 1836 Broadalbin, NY, Died: 1901
Spouse: Rebecca Plantz
Parents: Henry Kested and Phoebe Demarest
Siblings: None
Children: Anna, John, Charles, William, Gussie, Jessie, James, Harry, Bert, Bertha, Shelby

R/
Bob