If you wanted to unify the vampires into a single faction, could you turn the bloodlines into traits? So, if they are 'born' from a faction leader, they have 100% chance of getting that trait, and if they are randomly spawned, they have equal chance of becoming one of the 4-5 clans ? Each could come with anti-traits of the other clans, preventing multiple bloodlines from appearing on one character. This way you would have a Kingdom comprised of multiuple vampire families, although i'm not sure if this makes sense Lore-wise.

Otherwise, the Von Carsteins do sound like the natural choice for the Vampire faction from what you ahve described.