Kim, This is not my Keller line or they don't connect at least at this point. I belong to ancestry.com they have many records and it is pretty easy to find most families pretty easy, then it is just finding the death documents or obits to prove that you have the right family members.
Also on the California Death index there is a Leona E. Zeller b. 12 Nov 1886 in MN d. 4 Dec 1948 in Los Angeles, CA lists her fathers name as Keller and Mothers maiden name as Kippels
This death certificate should have the proof of the mother and father of the two girls.
I do get down to the Minnesota Historical Society in the spring and fall a few times and would be happy to copy the death records for you when I get there.I don't go there to much in the summer but this fall I would be happy to check out the death certificates or see if there would be obits for Matilda and Nicholas.