Iowa had mid-decade census records, which can be helpful in locating lost ancestors that may have passed away before the US census was taken. The following Iowa census records from 1915 are individual cards with the family member's name, age, education, occupation, residence and parents place of birth, etc which is very helpful in obtaining details about the family.
Ole and Mari Finnestad's eldest daughter Elizabeth had 10 children with husband Ole Andreas Knutson. I've been able to locate 9 of their 10 children; one was Mary (Maria) Berthea Knutson. Mary married Stephen Olson in Ogle County, Illinois on December 27, 1887.
Mary and Stephen had 7 children, (as far as I know from the conflicting census records). Their eldest was Orville Olson.
Orville Olson, born in Illinois before the Olson family left Ogle County, Illinois and moved to Iowa.
Orville's wife, Ida, born in Illinois, but married Orville while living in Iowa.
Orville and Ida's first child, Marvin Sanford, born in Cylinder, Palo Alto County, Iowa.
Orville and Ida's second child, Evelyn Ordell, born in Cylinder, Palo Alto County, Iowa.
Orville and Ida's third child, Alma Luella, born in Cylinder, Palo Alto County, Iowa.
From what I've been able to tell, these were the first great grandchildren of Ole and Mari Finnestad.