Johan Martin and Anna Gunelie Andersen

I am looking for some information about a brother and a sister from Trondhjem. I can't find them in the 1900 Norwegian census. Their names are Johan Martin Andersen/Anderson, born in 1865 in Lexvigen S. og P. and Anna Gunelie Andersen/Anderson, born in 1871 in Trondhjem. Their parents are Ole Andersen, born 1828 and Lorense Johnsdatter, born 1841/42. They have a sister, Laura Oline Anderson, born 1876/77, she went to America. Since I can't find them in the 1900-census, I guess they went to America too. Can anyone help me?