OFFERDAHL/OFFERDAL, Knudt Iverson

Hello! I'm a newbie, and I don't understand Norwegian. The Norwegian/English dictionary has been ordered but has not yet arrived. I am searching for children of Knudt Iverson Offerdal, born 2 Aug 1852 in Laerdal, the son of Iver Olsen Offerdal and Berthe Kristine Andfindsdatter also of Laerdal. He came to the United States in 1873, and in 1880 was living in Wahpeton, Richland, North Dakota, with a wife named Erma or Enna. In 1885, the wife had disappeared, and he was living alone across the river in Breckenridge, Wilkin, Minnesota. In 1990, he could be found in Tacoma, Washington; in 1903, Everett, Washington, and in 1921, became a naturalized citizen in Seattle, Washington. I haven't found any death record. Knudt is probably my great-grandfather, but I haven't proven it yet. He had one daughter out of wedlock in 1873 in Norway named Anna. I'm guessing as to the rest of the name. Perhaps Anna Knudtsdatter Offerdahl or Anna Knudtsdatter Seim? Her mother was Metta Kristine Tomasdatter Seim, who later married Ove Tomasen, Haereid. His second child, that I know about at least, was my grandfather, Frank O. Haraldson. Frank was born in Wahpeton, Richland, North Dakota in 1885, and was living with his mother, Gena Olsen, in Breckenridge, Wilkin, Minnesota, at the time of the 1885 Minnesota state census. Because I don't know Knudt's daughters second and third names for sure, I can't find her anywhere in USA records, but I know that she came to the US in 1893. She was born on 6 Jul 1873, just prior to Knudt leaving for America. I would like to find her descendants to compare DNA with my uncle through the Family Finder test. Thank you to anyone who can help me! My 90-yr-old uncle and 95-yr-old mother are trying to find out who they are before they die.