Hi. You write: "Looking for decendents of Peter & Bertha Olson(Olsson or Olsen). They had a farm in Pierce county, North Dakota, 1900 to about 1940's. Peter born in Sweden(1864-1943) & Bertha born in Norway(1871-1947. There were about 11 children."
Descendants of Peter and Bertha Olson would be descendants of their children. You seem to know the names of the children (as you have counted them, and you have seen the census data in North Dakota). Do you think that sharing those names (of the children) would be a good idea?
Perhaps you might want to list their birth dates and birth places (even if you know approximate dates that would help).
The 1940 census is being transcribed now. You indeed may find the names of grandchildren of Peter and Bertha Olson in that census. You seem to know how to search the census -is that right? Or do you need help with that?