Vampire: The Trio
The Event Theories
A rampaging group of Werewolves decimated the kindred.
A mage, possibly the Necromancer, wiped them all out with a spell gone awry or horribly right.
Some disease turned them all into kine with amnesia of their unlife as kindred.
They were all killed by Belial’s Brood.
An ancient vampire killed them all.
They all moved to another city.