County historical societies have information such as obituaries, cemetery records, and other family records that may not be available online, so be sure to contact them and ask for a search. They usually have researchers who know the area.The cost is worth it. Here is the website showing contact information for all county historical societies in Minnesota. http://www.mnhs.org/localhistory/mho/chsclo.htmlhttp://www.mnhs.org/localhistory/mho/chsclo.html
Cass County is where you know they lived. Staples Minnesota falls on the county line of Todd county and Wadena county.
Keep checking findagrave.com, since new graves are being added by volunteers every day.
These are the census years available for Minnesota, at a website like familysearch.org/search for example. 1885 (too early for you) 1895 (maybe just right? or too late?) 1900 1905 1910 1920 1930 1940