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Borgen is a Norwegian "farm" name( Borgen, Lom, Oppland, Norway). In traditional naming patterns the child has a given name, a paternal name and a location or farm name.
Translated from Norwegian to English Borgen means Castle.
The farm name would change if the person moved. Hans is the son of Lars living in on the farm Borgen would be known as Hans Larson Borgen. If he moves to the farm of Moen he would then be known as Hans Larson Moen.
This naming pattern started to die out in the mid 19th century in favor of inheritance of surnames from the father. Some families chose to drop the farm name ( i e Hans Larson) and others chose to drop the paternal name ( i e Hans Borgen) and it would not be surprising to find brothers choose different surnames as the naming pattern changed.