If you check Castle Garden arrivalshttp://www.castlegarden.org/
There was a Heinrich SANDER, age 34 tailor
Maria SANDER 28 and Richard 9mths all arrived on 8 July 1876 aboard the " Oder" from Bremen. All born Germany.
If it is the right family, then probably child Richard died before the twins were born.
I am not having much luck finding them in the 1880 census.