Vivec says: http://www.imperial-library.info/content/thirty-six-lessons-obscurity-and-deception
I though the 3 tribunals where considered Demi-Gods be cause they are mortal, but have Godly powers.?.?
Vivec is a true god, and wrote himself in history as that. He also is one of a select few to achieve CHIM, which the Is/Is Not realisation. To put it as simple as possible, you realise that you are everything, and everything is you, but retain your individuality and still see the "I" in the Wheel of Convention. Because of this, he seems completely insane, but everything he says is true.
Sotha Sil and Almalexia are gods, but not nearly as powerful as Vivec. They also never achieved CHIM. The Psijic Order, which Sotha Sil belonged to, opposed it. Almalexia was too brash, and would never accept something like CHIM. Vivec's mindset was most suited to it.
Depends on the culture and view. Many races believe that Anu (Stasis) and Padomay (Sithis) were the original creators. Then, for example, the land of Nirn was born when Lorkhan's heart was shot into the ocean. [img]http://www.gamesas.com/images/smilie/tongue.gif[/img] There are many gods if you wish to see it that way.
Anu is Stasis, the basis of mortals and aedra. Padomay is Change, the basis of the daedra. In between was the Grey Maybe of what could be, according to the Monomyth. Lorkhan either tried/convinced the Aedra to sacrifice themselves for the mortal world, and then the daedra refused and didn't sacrifice a part of themselves. This is why the Daedric Princes and Lesser Daedra are much more powerful and present than the Aedric gods and Lesser Aedra, since they made no sacrifice. Together, the Daedra and Aedra are the et'Ada which means Original Spirit.
In the TES universe it is perfectly possible to start a mortal and end up a god.
There are several ways to reach heaven.
Vivec achieved CHIM, but before that the Triune re-wrote history so that they had always been the Dunmer patron gods.
That is true. It's important to note, though, that you can become only a god, or achieve only CHIM. They are different states of being.