Complex sentence: All three are said to be descended from Gilleoin of the Aird, a Celtic dynast who lived in the early 12th century, and the chiefs of the Clan Mackenzie are said to have been settled at their great stronghold on Eilean Donan by 1297.
Split into simpler sentences: All three are said to be descended from Gilleoin of the Aird, a Celtic dynast who lived in the early 12th century. The chiefs of the Clan Mackenzie seem to have been settled at their great stronghold on Eilean Donan by 1297.