Complex sentence: 'Abd ar-Rahman ibn Muhammad, his father-in law.He maried Abd ar-Rahman's daughter, Guisti Fatima, with whom he had issue, a son, his future successor, Ahmad III ibn Abu Bakr.
Split into simpler sentences: 'Abd ar-Rahman ibn Muhammad, his father-in law. He married Abd ar-Rahman's daughter, Guisti Fatima, with whom he had a son, his future successor, Ahmad III ibn Abu Bakr.