In the 1900 census for Washburn, 777 Bayfield Street:
Larson, Louis, born Oct 1864 in Wisconsin
Larson, Nels, born Jun 1861 in Norway
Larson, Lena, wife, born Mar 1877 in Wisconsin
I think this is your Lars and Niels. It says Louis was born in Wisconsin, but that could be wrong. Lars and Nils were both "Grocers", this means they had a food store. Many people named Lars called themselves Louis in America.
Lars Larsen died in Washburn in 1922. Lena died in 1969.