Seeking Theodore Oltesvig emigrating 1886 to US

In searching in vain for emigration record of Theodore Oltesvig, in the US Census 1910 and 1920 in Montana listed as having emigrated from Norway in 1886, purportedly from Stavanger. Tobias Oltesvig's purported emigration in 1880. I believed him to be older brother to Theodore, but possibility that Tobias/Thomas may be same person and be father to Theodore... Iowa State Census 1895 lists Thomas Oltisvig, 40, Mary Oltisvig 36, Theodore 16, John 13, and Gerty 11 in the town of Webster. Iowa State Census 1905 lists Tobias, Mary, Theodore, John, Gertie, Bertha, Petra, Tom, Rachell, all Oltesvig, all in same household. I discovered now that there is a town of "Oltesvig" in Rogaland. Perhaps they may have taken the name of the location when they emigrated? I find a person named "Oltesvig" living on farm Nærbø in 1900 Norway Census, but doesn't seem to be any other family members. Am hitting dead-end on emigration records ... would appreciate any pointers or suggestions? Thanks very much, Carra Johnson Callies