Complex sentence: He succeeded, not without dispute, to the office after his father, Syedna Mohammed Burhanuddin, who passed away in 2014 and is the spiritual leader of 2.5 million people living in 100 countries.
Split into simpler sentences: He succeeded, not without dispute, to the office after his father, Syedna Mohammed Burhanuddin, who passed away in 2014. He is the spiritual leader of 2.5 million people living in 100 countries.