Well, Bella and Edward would probably still be main characters. Since it's Twilight - related, their relationship is central. They might be exploring new aspects of their relationship in this 'whole new life' scenario.
Jacob could also be a main character. He has a strong connection to Bella and the whole vampire - werewolf dynamic. In a new life situation, he could be dealing with changes in his role, like how he fits into the world now that Bella and Edward might be changing their lives.
Sometimes, it might introduce new characters along with the familiar ones. For example, if it's a fanfiction based on a superhero story, the main character from the original might be joined by a new sidekick they meet in their new life. This new sidekick could be a local from the new place they end up or someone else in a similar situation as them. They could then form a bond and go through adventures together.
It could be new characters created specifically for the fanfiction. Maybe a young vampire who is just turned and is trying to figure out their place in the Twilight world. Another might be a human who has a special connection to the supernatural events happening around them.
Edward and Bella are likely to be main characters. Since they are central to the 'Twilight' story, in a fanfiction about a living will, they could be involved in making decisions regarding the living will, perhaps related to their future together or the safety of their family.
Another possibility is that the fanfiction could introduce new characters who play a major role in the 'coming home' story. They could be new vampires or humans who have a connection to the original Twilight characters. For instance, a new vampire who was turned while Bella was away and now she has to deal with this new presence when she comes home, and this new character could bring a whole new set of conflicts and relationships into the story.
It's likely that Bella and Edward could be main characters. Since it's a Twilight fanfiction, they are central to the original story. And with the theme of 'broken hearts', their tumultuous relationship could be a focus. Maybe they are on a journey along the highways, either physically or in their relationship, and facing heartbreak.
In addition to the classic trio, we might see some new characters who are native to Australia in the fanfiction. Maybe an Australian wizard who becomes friends with Harry and helps him understand the new magical world down under. It could also be that some minor characters from the original books, like Neville, play a more significant role in this new Australian - based story.
Bella Swan is a very likely character. Since she has such a strong connection to Forks, which is her home in the Twilight world. Her journey home could be filled with thoughts of Edward and the vampires she has come to know.
Maybe an old storyteller who has a deep connection to the area with the cracked pavement and during twilight shares tales of the past with the younger generation. There might also be a group of friends who use the cracked pavement as their meeting place at twilight, and they get into all sorts of adventures together.
Since it's a Twilight fanfiction, it probably still features the main characters from the original series like Bella, Edward, and Jacob. But it might also introduce new characters related to this 'lottery of life' concept.
Obviously, Naruto would be the main character. Since it's about him being the new Kyuubi. And his friends like Sasuke, Sakura, Kakashi would also be important characters. They would likely be involved in how they react to Naruto's new state and how they support or oppose him.