Complex sentence: In 1928, Arlen married Countess Atalanta Mercati in Cannes, France, where he had moved to and where he had two children, respectively a son, Michael John Arlen born in 1930, and a daughter, Venetia Arlen, born in 1933.
Split into simpler sentences: In 1928, Arlen married Countess Atalanta Mercati in Cannes, France, to where he had moved. They had had two children, a son, Michael John Arlen born in 1930, and a daughter, Venetia Arlen, born in 1933.