Olsen Nord Odalen Ostvand farm question

I am searching in the Norwegian Historical Data Center for my great grandfather who was listed as being born in 1869. His name was Ole, and he had two brothers, Arthur (b 1862) and Carl (DOB unknown). Their father was Kristofer. All these spellings could have variations. I have Ole's US naturalization papers and with it or at the same time I acquired a copy of two letters written in 1866 recommending his father (?) for citizenship here. My family states that the three brothers came over (Carl and Arthur probably together in 1881, Ole followed in 1892) and, after their father Kristofer's farm failed, he joined his sons here. If this is true I don't understand why the recommendation letters were dated in 1866. But, anyway the name on one letter is Kristofer Olsen Ostvand and the other is Christofer Olsen S/Larkedalen (hard to read the old cursive). I think the Ostvand is a farm and perhaps the S/larkedalen is as well. I am trying to find Kristopher and family in the 1875 Norwegian census and can find the farm Ostvand but no Kristofers, Oles, etc. and can find several Kristophers, Oles, etc. but none related to Ostvand or Nord Odalen which one letter has on it. Can someone help with this?