Brian, you are spot on with everything! I am so happy and grateful you have unearthed these documents. I am struggling with not knowing Norwegian, and just beginning to find my way around the databases.
So Nils was from Fredrikstad after all! I wonder why they told me he was from Bergen.....
I do not as yet have any confirmation of Caroline Marie's birthdate. I have a burial date from Greenwood Cemetery, but they have nothing else. She is buried as "Marie Johnson" - It appears that she never used "Caroline" in the United States.I will make a trip to the cemetery to take pictures once I am reasonably certain I have located pretty much everyone. I am hoping that I can find Marie's death certificate in the NYC archives. Their collection of microfilms has had some losses over the years. In the censuses Marie's birthdate referred to variously from 1863 to 1865. You are also correct about using various forms of her surname - her mother Andrea did the same thing. Andrea (who was married in Glemmen in 1856, supporting the evidence of location you gave me) used Carlson, Andersdr, Engebretsen, and Morvetson, all on different documents.
I was also happy to learn the names of siblings from the 1865 census. I have a copy of a very old, quite fuzzy photograph, showing Nils about two or three years old, with his mother and sisters. I did not know there was an older brother, Johan L. Now the challenge is to track them down, and see if I have living relatives in Norway. I have been successful in this on my Swedish side, and it has been wonderful getting to know my (third) cousins. Thank you again!