Rognstad/Rognstadengen

Trying to trace my husbands roots- here's what we know: Martha Olsdatter Rognstad (DOB-11/12/1881) born in Oppland, (Gran Parish) came over with her son Einar Orien Rognstad (DOB-1/30/1904) in 1908. Einar's father, we are- told is Andreas Amundsen born in 1877- he and Martha were not married. We know nothing about him, his family or where he is from. We would love to find some information on him and his life and family. We have found Martha and her family in the 1900 Census in Brandbu on the Rognstadengen farm. We would also love to find out some information on Martha's parents and brothers. It would be exciting to see how far back we could go, who else came over-and to where -and who of our family is still there in Norway. Any information would be so greatly appreciated!!! We would be thrilled with anything! Thank you so much for your time and effort fo us. Lynn Rognstad