Complex sentence: The 18th Faatemi Imaam Maulaana Mustansir Billah (478 AH/1094 AD), from the Aal-progeny Mohammad ul-Mustafa, held the seat of the Faatemi Empire in Egypt and acted as the sole authority of the Shi'a Isma'ili branch of Islam.
Split into simpler sentences: The 18th Faatemi Imaam Maulaana Mustansir Billah (478 AH/1094 AD), from the Aal-progeny Mohammad ul-Mustafa, was holding the seat of the Faatemi Empire in Egypt. He was acting as the sole authority of the Shi'a Isma'ili branch of Islam.