Thank you very much!! These were really helpful. The 1900 census does not fit perfectly, as it states that Mathilde Hansen´s father was born in Norway and that her mother in Denmark; it was in fact the other way around, which I guess is an acceptable mistake. The 1910 Census puts this back correctly. Therefore I am pretty sure now that I am on the right track!
The 1920 census supplied me with some new and interesting names (in-laws). And the naturalization document was great!