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.
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.
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.
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.
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.
Without knowing the actual story, it's difficult to determine the main characters. However, if the story is focused on the concept of women sleeping, the main characters might include the women who are sleeping, of course. But it could also include people who are affected by their sleep, for example, a husband who is worried about his sleeping wife, or a child who is curious about the sleeping mother. There could also be antagonists in the story, perhaps someone who wants to disturb the women's sleep for some malicious reason.
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'.
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.
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.