It appears that the "bloodline" idea is due to the nature of a monarchy; the monarch's descendents usually have the most claim to the throne. And Mankar Camoran was the heir to the ancient Camoran Dynasty.
Yes, and through the Camorans, quite potentially the Ayleids as well. But I don't see how Mankar could be prominently related to the Remans (other than the common-variety sort of "related" as with the Septims, where after so many generations, most people can realistically claim some small amount of Septim blood). I have seen no source to identify a connection to the Remans.