Denu Family,Michael&Barbare/Gates Ny

Trying to find Michael& Barbara Denu, Immagrated from Germany abt 1856-1860, found them on 1860 census,name spelled Danough, may have spelled the way it sounded,unale to find when they died,checked census for 1870, 1880 & 1900,no luck, they had three Daughters,Catherine 1846-Germany,Frances 1848-Germany,Helen 1850-Germany,Margaret 1858-New York State-would like to know when they died and where they are buried.