Being a Legendary Rank did not mean one was invincible. It just meant they wouldn't die so easily and had absolute power over the ones below.
They weren't omniscient and couldn't be omnipresent either.
The founding father could not keep everyone in check. He tried to do damage control but it was too late.
One of the wives who was a vampire slept with another vampire and gave out the secrets of the Asuras she knew.
The development was rapid and the woman made her children kill the Asuras who did not belong to her lineage. The Asuras were technically humans and natural prey of the vampires.
The vampires powered up and developed alongside the Asuras.
The founding father had to work very hard to exterminate the vampires and stop the internal struggles of the clan.
Before he could solve all the problems, he was ambushed and killed by the vampires.
