The main characters are likely to be the ones from the original 'Twilight' like Bella, Edward, and Jacob. In fanfiction, they might be portrayed in different lights or with different personalities.
In the 'twilight 2008 fanfiction', the main characters would be those from the 'Twilight' series. Bella Swan, the girl who moves to Forks and becomes the center of attention. Edward Cullen, the brooding vampire who falls in love with her. Jacob Black, the werewolf who also has feelings for Bella. However, some fanfictions might introduce new characters that interact with the originals, but these three are usually the foundation of most stories in this fanfiction realm.
Typically, in a 'the walkers twilight fanfiction', we might see the protagonists from 'The Walkers' being thrust into the Twilight world. So, it could be characters like Rick or Michonne. Alongside them, the Twilight characters would also play significant roles. Bella might be involved in some sort of encounter with the Walkers, and Edward could be using his vampire abilities to deal with the new threat or situation that the Walkers bring to the Twilight universe.
Typically, the main characters would include Bella, Edward, and the other members of the Cullen family. Since it's a Twilight - related fanfiction, they are likely to be central to the story. However, new characters might also be introduced, perhaps someone who is related to the Twilight Key in a special way, like a guardian or a seeker of the key.
Well, it could be a new vampire that the author has created. This vampire might be a loner, living in the shadows away from the main vampire clans in Twilight. Another could be a human character who stumbles upon this hidden vampire world.
There might also be an older, wiser character, like a mentor figure. This character could guide the younger protagonists, sharing their wisdom and experience about the strange happenings in Blackwater. Their insights could be crucial in solving the problems that the characters face in the fanfiction.
It's hard to say without reading it, but it could be Bella and Edward. Since it's Twilight fanfiction, they are often central characters. Maybe the vow involves their relationship, like a vow of eternal love or a vow to protect each other from new threats in the story.
Another type of main character in these fanfictions could be a human who becomes intertwined with Benjamin's life. This human might be in a dangerous situation that only Benjamin can save them from, or they could be someone who has an unexpected bond with Benjamin. This creates a lot of drama and interesting plotlines as the relationship between the human and Benjamin develops, often against the backdrop of the vampire - human relations in the Twilight world.
Obviously, Darkward is a main character. There might also be characters from the original Twilight series like Bella or Edward who interact with Darkward in unique ways in the fanfiction.
There could also be new characters introduced in the 'Fourteen Twilight Fanfiction'. These new characters might be other vampires or werewolves with their own unique powers and personalities. They could play important roles in either helping or hindering the main characters in their relationships or in dealing with the various challenges in the story.
There might be a young and rebellious wolf in the pack who challenges the traditional ways. This character can bring a lot of drama and new ideas to the story, as they constantly butt heads with the more conservative members of the Twilight Pack.
I don't have enough information to know the main characters. It could be the phoenix itself as a main character, or perhaps there are other characters that the phoenix interacts with, like a wizard or a fairy.