Complex sentence: His first wife, Janina (née Dłuska, b.1909), whom he had married in 1944, had died in 1986; they had two sons, Anthony (b.1947) and John Peter (b.1951).
Split into simpler sentences: His first wife, Janina (née Dłuska, b.1909), whom he had married in 1944, had died in 1986. They had two sons, Anthony (b.1947) and John Peter (b.1951).