Nicolai Benjamin Cappelen was the first child of
Ulrich Fredrich von Cappelen (1770–1820) and his wife Benedicte Henrikke, née
Aall (1772–1812). His namesake and maternal grandfather was
Nicolai Benjamin Aall. As such his group of uncles included Constitutional founding fathers
Severin Løvenskiold,
Jacob and
Jørgen Aall and their brother, cabinet minister
Niels Aall. Also his father's brother
Didrich von Cappelen was one of the Constitutional founding fathers in 1814. Nicolai Benjamin's younger brother
Ulrik Frederik Cappelen too became a jurist and member of the national parliament. The second brother, Wittus Juel, became a merchant in
Drammen. The oldest sisters Didricha and Louise were married consecutively to bishop and politician
Jens Lauritz Arup. The fourth sister Benedicte married their cousin Hans Blom Cappelen; from this marriage, Jørgen got a nephew
Didrik who became a member of parliament, and a niece Marie who married
Fritz Trampe Flood of the notable Flood ship-owner family. His third and youngest brother
Jørgen Wright Cappelen became a book publisher. and had no children. He left parts of his great book collection to the Skien school library and parts to his cousin Erik Johan Cappelen of
Borgestad Manor, who was his assistant for a period. ==Career==