It might be a good idea to have a list of optional powers, each of us being able to choose our own or make our own up as long as its directly related to vampire lore either TES or otherwise.
Heres my basic understandng of vampires powers in TES:
Generic (found in all vampires)
-The ability to create more vampires
-Immortality
-Greater amounts of strength
-Higher potency in regards to magicka
-Heightened senses and reactions
-Greater speed and agility
Clan specific
-Vastly greater strength on top of generic traits (Quarra, Morrowind)
-Vastly higher potency in regards to magicka on top of generic traits (Aundae, Morrowind)
-Vastly greater speed and agilit on top of generic traits (Berne, Morrowind)
-The ability to freeze liquid (icluding internal bodily fluids) by breathing on them and the ability to pass through ice without breaking it. (Volkihar)
-The Ability to disintergrate into a mist that can also travel through water (Keerilth, Valenwood)
-The Ability to swallow men whole (dont ask me about the logistics of this one
They are native to Valenwood so perhaps the men arent that big.) (Yekef, Valenwood)
-The ability to devour and take the appearence of childeren (Telboth, Valenwood)
It might be a good idea to either add new powers to each clan as the Blood Matron grows more powerful or simply increase the strength or effects of the powers.
If you where going to increase thestrength of the powers over time it might be a case of the Volkihar or Skyrim being able to eventually freeze any object and pass through any object instead of just liquid and ice or the Telboth being able to assume the form of larger humans mer and beastmen rather than just those small in stature.
Ether way if you keep the powers of the vampires specific to each clan it would allow those playing as vampires to have as much variety of choice as those playing were critters.
as for Cyrodillic vampire clans I managed to find this
It suggests that there is infact a clan in Cyrodiil we just dont know their name. Sine the Dark Blood guild is situated in the Jerall mountains it could be safe to assume (for the intents and purposes of the RP) that we are infact the vampire clan of Cyrodiil.
EDIT:
Forgot this
Folklore (not limited to tes) powers:
-The ability to turn into mist.
-The ability to pass through walls.
-The ability to shape shift into any innanimate object at will (usefull for spying on people or hiding)
-The ability to shape shift into animals insects fish and reptiles that are not bigger than the Vampire (I.e No horses or elephants or large cats/bears)
-The ability to scale walls (we've seen this one in alot of vampire books and movies)
-The ability to hypnotise and control minds through either magical means or by litterally enthralling the victim with the vampires own beauty.
-The ability to curse live stock and crops (not exactly a usefull ability for an RP but it exists in folklore)
-The ability to steal organs (Again not so usefull but it exists.. for whatever purposes)
Now as we can see most of these folklore powers have been taken and adapted into the TES vampire Genology to certain degrees so it really limits using outside powers from folklore to a certain extent.