Vampires: These were humans previously, but when vampires had bitten them, then they became immortal.
Werewolves: These are Indian descendants; you can see Jacob and his people are tanned.
Humans: They are real people like you and me.
These three are interrelated in terms of conflicting relationship, for instance Jacob and Edward have a settlement that none of them would come to other’s area, and they do not like each other’s smell and are enemies for ages. As far as humans are concerned, they believe that werewolves do not hurt humans and even humans can marry them as they have capacity to transform into human shapes. Thus, werewolves have similarities with humans. Vampires, on the other hand are outsiders and humans fear them and werewolves dislike them. But Cullens have different story, they neither suck human blood nor hurt them, instead they are vegetarians. So, three are somehow related with one another.