User blog comment:KillHil/Assassin’s Creed III Ventures into the Wild/@comment-69.146.244.153-20120407200709/@comment-1153722-20120409121846

Matt Turner confirmed in an interview with EscoBlades that none of Desmond's ancestors are related to each other. So Aquilus, Altaïr, Ezio and Connor do not come from a single bloodline, but their bloodlines converge at some point which eventually passes into Desmond.

Take a look at your own family tree, or think of how your grandmother from your mother's side isn't related to your grandfather from your father's side. Everyone is a conversion of many different bloodlines. Altaïr, Ezio and Connor are all coincidentally descended from the First Civilization, but they are not related to one another.