Complex sentence: They married on December 21,1952, despite the opposition of her aristocratic family, and during the following 18 years they wrote over 700 letters, including a very active exchange with Hermann Lenz and his wife, Hanne.
Split into simpler sentences: They married on December 21,1952, despite the opposition of her aristocratic family. During the following 18 years they wrote over 700 letters; amongst the active correspondents of Celan wer Hermann Lenz and his wife, Hanne.