1. Succubi In PC1, Stephenie Meyer mentions the Denali coven: Tanya, Kate, and Irina had an interesting path that led them to "vegetarianism": they are the originals behind the myths of the succubus. Their fondness for human men eventually led them to feel remorse for their victims, and they slowly trained themselves to resist human blood.
This coven hasn’t played a significant role in the story as it has been edited out, although the myth of the succubus is well recorded elsewhere. A succubus is a demonic seductress who preys on human men, drawing energy from the men to sustain her existence. In the case of a female vampire who is a succubus, she would normally draw blood from the man she has seduced. The Denali coven has broken from this tradition and the sisters live on animal blood just like the Cullens.
2. Enemies of the werewolf In the Twilight universe, the main threat to the vampires comes from the werewolf. As Jacob Black explains to Bella, "The cold ones are the natural enemies of the wolf." (TW6), and he is also clear that the Quileutes are historically linked to "the wolves that turn into men, like our ancestors." (TW6) Some of the younger members of the tribe don’t seem to believe the legend, and dismiss it easily. Jacob says, "So, do you think we’re a bunch of superstitious natives or what?" (TW6), but he also points out that his father believes it. There is a definite lack of trust in this relationship, even though the Cullens feed on animals. "There’s always a risk for humans to be around the cold ones, even if they’re civilized like this clan was. You never know when they might get too hungry to resist." (TW6)
A treaty has been created to ensure that the Cullens stay away from the Quileutes and their land. "The Cullens don’t come here."(TW6) The Quileutes will never reveal what the Cullens are, as long as they never set foot on the reserve. Edward’s absence at La Push supports this, however Jacob, by telling Bella the story, has inadvertently broken the treaty.