"and what happened after the death of Marcus and William? did all the Vampires and Warewolves die? so why didnt Kate and Michael die?"
*just saw it* I think what happened is that the curse of vampirism and Lycathrophy was simply removed, meaning those infected were no longer vampires are werewolves. Meaning Michael is likely just a human again, but not sure.
If they supposed to die Selenie still wouldnt' have died because she took in blood from the first immortal, but I am not sure what the first immortal 'was' to be honest. Was he a vampire? A Lycan? Something else?
Edit: also...IMO that movie could have almost been rated NR-17...just because of that one 'scene'. They could have done that scene a bit less 'obvious'....
The first one explains who the first Immortal was. The Lord Corvinus. He wasn't vampire or Lycan. He had three children, one bitten by a bat, one bitten by a wolf, and the other lived the life of a mortal.
You really need to pay attention to the crazy doctor guy ;)