Complex sentence: Al-Husseini was the scion of a family of Jerusalemite notables, who, after receiving an education in Islamic, Ottoman and Catholic schools, went on to serve in the Ottoman army in World War 1.
Split into simpler sentences: Al-Husseini was the scion of a family of Jerusalemite notables. After receiving an education in Islamic, Ottoman and Catholic schools, he went on to serve in the Ottoman army in World War 1.