Gulbrand Gulbrandsen or Gilbert Gilbertson in ND

Gulbrand Gulbrandsen born in Kongsberg (Gransherad) on March 18. 1856, married to Maren Karine Mathiassen, b on January 28. 1856 in Vaale, Vestfold County, Norway. They emigrated to Amerika between 1882 and 1884, They had 2 sons in Norway, Godtfred, born on July 18. 1870 and Kristian, born on March 3. 1882 - so they left after his birth, They lived in Holmestrand from 1881 till 1882. I can not find them in any passengerlists. They had possibly 7 more children in the US, probably in ND. I would like to find living family descending from these immigrants - but how can I find them? Turid Engh