I am not sure what context this is in, but great father and great chief could refer to a fatherly figure to Lewis, or it could be a religious reference such as a God/ the Lord?
As of 2009, Sunni Muslims constituted 87–90% of the world's Muslim population-
the Shia believe that leader is called an imam and this "caliph/imam" should be a direct descendant of Mohammed-
and I have no clue on the last one