Gunderson ancestors

I am trying to find more information on my g.g.grandfather Gunder Niris. married to Maren Hansd. according to 1865 telling. My g.grandfather was his son Nils August who emigrated to MN in 1892, and settled in chokio, stevens county MN. Gunder was born in Saude Prgj. and Maren was born in Boe Prgj. Nils August was born in July 1859 in Skien. Looking for sibilings of Nils, and Gunder and any other information reguarding them. Nils married Hansina Marie Gunilda Hanson( born in chicago, IL in 1865 and moving to norway at the age of 9) in oct 1888 in skien. Any info on her mother Hanna Hanson would also be appreciated.