Greatest House..?
While the Great House Telvanni is a dysfunctional gathering of nerds, it is also a Dunmer noble house - those scary, mafia-like organisations who have distributed the whole of Vvardenfell among themselves and engage in subtle, long-running plots of blackmail and murder to pass their time.
Certain manners are expected of anyone who choses to participate. If you are not sure you can make polite conversation among nobility, you should read up here. To make yourself familiar with the subtleties of Dunmeri etiquette in particular you can check here.
Smart mer don’t deal with these kinds of people because they happened to be in the neighborhood. Stupid mer die young.
To stress the Mafia clan analogy once more - while there are perfectly valid reasons to get involved with one, it’s common knowledge that this kind of association ends only with ones death - at the earliest.
Almost every person in Morrowind is associated with a House in one way or another. Be it that their grandparent used to be a Retainer or the mayor of their village takes bribes, you don’t have to go far to find the influence of a Great House in various degrees of subtlety. Bribery, blackmail, intimidation and manipulation are the average tools in the Game of Thrones Houses.
Why does your character make this choice?
Political pick-a-stick
There used to be six Great Houses, but nobody mentions House Dagoth anymore.
The official version of the story is that they allied with the Dwemer in the Battle of Red Mountain, some six millennia ago, and were wiped out by means of retribution. Since even their name is considered taboo finding the truth is… difficult.
House Dagoth serves as constant reminder to any of the other Great Houses what happens when their peers unite against them. This leads to an unstable peace where the players do not act against each other directly but rather settle their conflicts (mercantile, political or territorial) by proxy.
If a player is seen moving it means his action will be anticipated. Jostling the sticks will result in a lack of prestige.
Direct assassinations between rivalling Houses are by Gentlemers’ Agreement ever executed by a Morag Tong. Directly murdering members of any House but one’s own will result in a tragic accident.
First among equals? Nah. Infighting!
This information might change after Morrowind release
In our setting, we have three branches of the Great House - Vvardenfell, Port Telvannis on the Telvanni Isles, and Central Morrowind - ours.
Telvanni Isles
… took a bad beating during the Akaviri invasion (click here for non-canon background detail), but is quickly recuperating.
Our setting’s headcanon:
Here is where the stakes are highest. Some consider a position in Port Telvannis a success, but effectively it means the end of everything that makes life enjoyable as the power struggle becomes a full-time occupation.
Telvannis is a snake pit, and the only reason that they aren’t all dead by this point is that every single one of them is paranoid.
Vvardenfell
This information will change after Morrowind release!
Our setting’s headcanon:
The Telvanni are a strong presence on the island, since the other Houses are rather focussed at the mainland and their Pact of the Pitiful right now, leaving the Telvanni largely unsupervised. There is an Archmagister, and there is a council, although they aren't doing much - everyone is far too busy nerding to meddle with the affairs of their peers.
The towers are grown too far apart to make poisoning and backstabbing a viable method of solving conflicts when it's far more feasible to just avoid them for the next few decades - until you need something, that is.
Central Morrowind (that’s us)
Formed in 2E 582 (according to UESP two years after the beginning of the Three Banner War and before various other events that will not be elaborated due to spoilers), the Central Morrowind Branch is the youngest and weakest seedling of the Great House.
Heimlyn Keep is the only organised Telvanni presence on the Mainland and as such subject of everyone’s close attention to make sure that the spores don’t spread. The Archmagister makes sure that everyone sees them as good neighbours - she might even be a little too successful, as people are wondering if Telvanni’s hands are not a little too clean…
What does that mean for our characters?
Tl;dr:
Skyrim - 5 Telvanni Facts - Elder Scrolls Lore by FudgeMuppet pretty much summarizes what the Great House Telvanni is and what its members are about. Though this is only general information on the Great House based on lore - be sure to read additional information on our setting, since it can occasionally divert from general consensus.
