I've been trying to find the Schoharie NY Coss as well. This is what I have documented--

My 2 great grandfather Peter Coss 1815-1885 m Emily Broad 1815-1879. Emily is the daughter of Hezekiah Broad and Harriet Waite. Peter Coss and Emily Broad Coss are buried in Zion Rural Cemetery Seward Schoharie NY.

1840 Census NY Delaware Masonville Aaron G Broad living nearby 1 male under 5, 1 male 20-30, 2 females 20-30
1850 Census - Seward, Schoharie Co., NY
Peter Coss (35) living with Hooper (65) and Polly (60)
1860 Census - P.O. Carlisle, Seward, Schoharie Co., NY - Enumerated 23 July Peter Coss (45) farmer; Emily (45); Hester ( ); Rosanna (14); Oscar B. (11); Olive (8); Zelotis W. (5); David (3)
1870 Census - P.O. Seward, Schoharie Co., NY - Enumerated 28 July David is now listed as Hiram (13) All other family members are the same. All born in NY.
1880 Census - Seward, Schoharie Co. Peter, Rosanna, and Oscar are living with Peter's brother, Hiram.

Zelotus Coss 1854-1918 m Harriet Adele Watrous 1867-1948. Zelotus was born in Schoharie Co but lived in Bainbridge Chenango NY for his adult life.
I thought that Hooper (Hybertus) was the father of Peter, but now I'm not sure as the children don't match up.