Complex sentence: The Otaibah tribe are the descendants of the mighty Pre-Islamic tribe of Hawazin, that is of the Qays ʿAylān, that is of the Adnan, who are Ishmaelites, and descendants of Ishmael, the elder son of Abraham.
Split into simpler sentences: The Otaibah tribe are the descendants of the mighty Pre-Islamic tribe of Hawazin, that is of the Qays ʿAylān, that is of the Adnan. An Ishmaelite tribe who are descendants of Ishmael, the elder son of Abraham.