These two families were listed on 1880 census. You mentioned that you had seen 1870.
Roberta

1880-Suffolk County, NY - Setauket Page 59B
David BRISTOL - Blk 41 Born:NY
Angelene - Wife 39 B:NY
Isaac - Son 19 B:NY
Amelia - Dau 17 B:NY
Elliott - Son 12 B:NY

Listed just before Bristol Family on page 59B
Henry WOODHULL - Blk 53 B:NY
Catherine - Wife 42 B:NY
Alberta - Dau 18 B:NY