Thank you mague

Thanks Jan

Thank you driosketch

You don't need to have the actual quest and meet the quest NPC (in any of the "Faction Zone 5" capital cities - Evermore in Bangkorai, Riften in The Rift, Rawl'kha in Reapers March.) Once you have the disease, you can go to the relevant vampire or werewolf shrine directly, there should be a blue quest arrow over the scroll you need to read to get into the preliminary vampire/werewolf quest.

You have not stated your FACTION yet - are you:

(1) Daggerfall Covenant? In that case, look in Bangkorai. The vampire altar is on the west side of the province, between East Evermore Wayshrine and Pelin's Graveyard, just west of the crossroads which is southeast from the wayshrine. The werewolf shrine is on the eastern side, just follow the lake shore northwards from the tower-delve of Viridian Watch. The "Forsaken Stronghold" player house is nearby, but on the other side of the rocky ridge.

(2) Aldmeri Dominion? In that case you should be in Reaper's March. The vampire altar is right by the World Boss of "Ushnak's Rest", in the northeast corner, north of Pa'alat and west of Fort Sphinxmoth. The werewolf shrine is only a little further to the northeast in distance, but on the other side of a rocky ridge, it is easier to reach from Fort Sphinxmoth.

(3) Ebonheart Pact? Both are on the eastern edge of The Rift. The vampire altar is right in the northeast corner, just across from the road that crosses into Eastmarch, northeast of Shor's Stone. The werewolf shrine is further south, on the other side of the wall that gives Fort Greenwall its name, almost directly east of the "Hunter's Glade" player house.

So the actual early stages are:

(1) Be in Bangkorai, Reapers March or The Rift.

(2) Get bitten by a Werewolf that gives you Sanies Lupinus, or a Bloodfiend that gives you Noxophilic Sanguivoria. It used to be the case that you had to do this at night during a Full Moon for wolf, or New Moon for vampire. However, it is not always certain that this is still the case, and if it isn't, it isn't even certain whether this is deliberate or a bug.

(3) OPTIONAL: Head to the province's capital city (Evermore, Rawl'Kha or Riften) and look around for a man with a blue quest arrow (resembling a Daily Quest rather than a Sidequest) over his head, to talk to. He will tell you either to find a priest (who is somewhere in the city, usually in either a major temple or the Mage's Guild) to cure it, or to go to a shrine to have your status as a werewolf or vampire confirmed. REPEAT: YOU DO NOT NEED TO DO THIS PART AT ALL.

(4) Follow the directions given above - and the players heading to and from the relevant spot - to find the Werewolf or Vampire shrine. There will be a scroll at that place, also with a blue "looks like a daily quest" arrow over it.

(5) Read that scroll, enter the portal, do the mini-quest, gain the skill line.

You are correct, you CANNOT have both Vampirism and Lycanthropy (or their preliminary diseases, Sanies Lupinus or Noxophilic Sanguivoria) at the same time. You cannot even convert directly from one to the other: if you want to switch to the other, you need to get fully cured of the one you have (which will refund all skill points spent on its skills. Also, Vampires are generally Magical while Werewolves are an almost entirely Stamina creature, so if you have the stats to be any good at one, you'll be useless at the other, so switching from one to the other is not really recommended without a full skill respec.

An alternative way to get Lycanthropy or Vampirism: Travel to the relevant shrine (in one of the above provinces) WITHOUT having the preliminary disease, and ask another player to bite and infect you (this requires them having spent a skill point in a passive skill which can only be used every 7 days, and is acquirable at level 6 in the Werewolf or Vampire skill line.) This infection can only be passed on if you are already at the relevant shrine. To receive it, CROUCH, and the other player will have the option to bite you. After this, you are already at the correct shrine so you don't need to go anywhere, you can read the scroll and enter the portal right away.

Another note: If you decide get cured, and then later decide you want the disease back again, you will have to get bitten (by monster or player) and then go to the shrine again. You will retain your progress (from 1 to 10) in the Vampire or Werewolf skill lines, and thus be able to immediately re-spend any skill points you had previously spent - provided you actually have the skill points to spare and haven't spent them elsewhere. Progress in the skill-bar skills is likewise retained - as long as you spend the skill points on them. (Note also that the basic skills - "Feed" for vampires and "Devour" for werewolves - are free passive skills and do not require a skill point. The actual transformations, into Werewolf form or Vampire-Lord form, are likewise free in their original form - you still need a skill point available to morph it, if it's levelled up to morphable - and must occupy the Ultimate skill slot, both in human form and in Transformed form.

- Vampire skills can actually be used while in human form, without needing to use the Vampire-Lord transformation. The more Vampire skills you have on your skill bar, the faster your overall skill-line of "Vampire" will increase from 1 to 10 as you gain experience.
- Werewolf skills can ONLY be used in wolf-transformed form. They have literally nothing to do with how fast you gain skills in the "Werewolf" line: the only thing that increases THAT, is actually making kills while in Werewolf Transformation form, not in human form. If you are in a Group, then kills by groupmates may count: however if you have a Companion, kills by your Companion do not count (yes I have tried this), nor do kills by lingering ground effects (e.g. the poison gas effect from wearing Leeching Plate armor.) And yes, I confirmed all this yesterday by levelling up a werewolf.
- Both sets of skills can be put on either of your two skill bars in human form, for the purpose of levelling that skill up, regardless of whether you can actually use that skill or not. So for werewolves, it is a wasted slot but the skill can be levelled to max.

(Note you only gain experience in the skill if it's on the skill-bar currently in use at the moment of gaining experience points - e.g. killing a monster, or cashing in a quest. You can level up the skills by filling your skill bar with them when you do your daily crafting, for instance - or having a front-bar skill setup for doing a Random Normal Dungeon and having your beastform skills on the back bar, then switching to the back bar just before the final boss dies so that all the experience goes to those skills.)