Complex sentence: The proponents of the Abdalwadids claimed that Yaghmurasen descended from Idris II, the son of Idris I and founder of the Idrisid dynasty which would have made him a Sharif, i.e. a descendent of Muhammad, the prophet of Islam.
Split into simpler sentences: The proponents of the Abdalwadids claimed that Yghmoracen descended from Idris II, the son of Idris I and founder of the Idrisid dynasty. Something that would have made Yghmoracen a Sharif, i.e. a descendent of Muhammad, the prophet of Islam.