Need help with info for great-grandparents

I hesitate going back to all of you since you have been so generous with your expertise and time, but I am so excited about what I have recently learned I cannot resist. I have very little to go on with this set of great-grandparents. My great-grandfather is Michael (many spellings) Mathiason born in 1842 somewhere in (western I think) Norway. My great-grandmother Pernella or Nelle Swenson was born 7 Oct 1848 in Norway. Her obituary says her birthplace was Berien, but I can't find such a place; I wonder if it was transcribed wrong and maybe should be Bergen. A set of portraits exists of the couple taken in Oslo before they left Norway in 1865. They were married 16 Jan 1871 in IA. They farmed in Thor, IA and had 10 children. The children are Carl, Amelia, Albertina, Julius, Lorensi, Benhardt, Anna, Peter M, Nelle Alise, and Hannah Violet. Michael abandoned the family and no one has any idea of what happened to him. The story is he ran off with another woman. Nelle is buried in Blossom Hill Cemetery near Thor, IA the actual address is Badger, IA. I have looked at all of the US censuses regarding these people, so I do have more info about their lives here. I don't know if it's possible to find out anything of their lives in Norway. Please let me know. Thank you!