Well, Bella and Edward are almost certain to be involved. In Twilight, they are the central couple. In a fanfiction with this title, their relationship could be further explored, especially if something happened to Bella while she was sleeping that affected their bond.
Jacob could also be involved. He has a complex relationship with Bella in the original story. In this fanfiction, he might react in a different way if Bella was in a sleeping state. Maybe he tries to protect her while she's unconscious or has a different view of the vampires' actions during this time.
Obviously, Edward himself is a central character as he is the one being wrongly blamed. Bella would also be involved as she is closely associated with Edward in the Twilight series. His vampire family, such as Alice, Jasper, Emmett, Rosalie, Carlisle and Esme, would likely be part of the story too. They would either be trying to help him clear his name or be affected by the false blame in some way.
The Princesses, Celestia and Luna, are likely to be part of it. They might be the ones with the knowledge or power to help Twilight. Celestia could offer her wisdom on how to control this new and dangerous ability, while Luna might use her connection to the night and dreams to figure out if Twilight is under some sort of spell.
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.
One interesting plotline could be a different take on the relationships between the characters. For example, how Bella's relationship with Edward might develop in a more complex way. Maybe she discovers new aspects of his vampire nature that were not explored in the original story while she was in a coma - like in a 'while you were sleeping' type situation.
Alice and Jasper could also be involved. Since they are both vampires and part of the Cullen family, an arranged marriage might be used to strengthen their bond within the coven or to establish some sort of connection with another vampire group. And Alice's visions could add an interesting twist to the story of an arranged marriage, as she might see the future implications of it.
Definitely Harry Potter himself. He's the central character in his own series, so it's likely he'd be involved in any crossover. Hermione Granger could also be a key character as she's smart and curious, and would be interested in learning about the 'Twilight' world. From 'Twilight', Edward Cullen is an obvious choice. His brooding nature and unique abilities would make for interesting interactions with the 'Harry Potter' characters. Also, Jacob Black could be involved, especially when it comes to the 'imprint' aspect as he has his own story arc related to that in 'Twilight'.
Obviously Naruto himself is the central character as it's about his hibernation. His friends like Sasuke and Sakura are also likely to be involved. They would probably be the ones most concerned about his condition and try to figure out what happened.
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.
Jacob Black could also be a main character. His relationship with Bella and the werewolf pack's connection to the Cullens might be explored in a new light in this fanfiction. Maybe his transformation or his knowledge of the supernatural world comes into play earlier than in the original story.
Bella and Edward are often main characters in such fanfiction. Since their relationship is central in the original Twilight series, in fanfiction about sacrifices, they could be the ones making sacrifices for each other. For example, Edward might sacrifice his vampiric nature to give Bella a more 'normal' life if she so desires.