Detlef married Johanna Sophia Elizabeth Oloff. Johanna was born the 26th of april 1861 in Rotterdam, The Netherlands and she died on the 2nd of november 1933, also in Rotterdam. They married on the 24th of july 1878 in Rotterdam, The Netherlands, and Detlef died on the 22nd of january in 1919, also in Rotterdam. (I can assure you that this is true, Johanna and Detlef were my father's grandparents)
Can you keep me up about your further search? I can't find much also about my Danish ancestry.