Prince Christian of Schaumburg-Lippe (1898-1974) was the son of Prince Friedrich of Schaumburg-Lippe and Princess Louise of Denmark. He was engaged to Princess Irene, but the engagement was broken before the marriage took place. In 1937, he married Princess Feodora of Denmark.
Princess Elisabeth of Schaumburg-Lippe (1908-1933) was the youngest child of Georg II, Prince of Schaumburg-Lippe and his wife, Princess Marie Anna of Saxe-Altenburg.
Elisabeth married twice. In 1928, she married and divorced Benevenuto Hauptmann. Two years later, she wed Baron Johann Herring von Frankensdorf.
I am assuming that the postcard is of Prince Christian and not his Elisabeth's brother, Prince Friedrich Christian, two years her senior. The photographs were taken by the same photographer in Hanover. If I am wrong, someone will let me know.