Bella's nightmares can also show her struggle with her new vampire identity. If she has a nightmare about not being able to control her thirst, it ties into her character's journey of self - discovery as a vampire. She was always a bit of an outsider as a human, and now as a vampire, she has new challenges to face. Carlisle's nightmares about his past sins are very much in line with his character. He is a morally upright vampire, constantly trying to atone for his past actions. These nightmares are a reminder of the internal conflict he has between his past and his present self, and how he is always striving to be better.
They can also expand our view of their relationship. Fanfictions about nightmares might introduce new scenarios where their relationship is tested in ways not seen in the books. For example, a nightmare where Edward has to choose between Bella and his vampire family can show how complex their relationship is, as it involves different loyalties.
Often, it starts with an unexpected encounter or a moment of realization. Maybe Carlisle sees Bella in a new light, not just as Edward's girlfriend but as an individual with her own charm. Then, there are small gestures of kindness and understanding between them that gradually build up the relationship.
The Cullen family members are important characters too. Edward, for example, might have an interesting dynamic with Bella in this fanfiction. He could be either protective or jealous of Carlisle's special relationship with her.
Maybe Carlisle and Bella could bond over their shared experiences of being different from the norm. Carlisle is a 'vegetarian' vampire, and Bella is a human who is in love with a vampire. They could have deep conversations about how they both struggle to fit in with their respective worlds and find solace in each other's understanding. This would add a new layer to their relationship and make it more unique.
It would likely shock and confuse many characters. For example, Edward would be very surprised and perhaps a bit jealous as he had a strong relationship with Bella. The Cullens as a family might be divided in their opinions. Some, like Esme, might be more accepting and try to understand, while others could be more hesitant. The werewolves would also be affected. They might see this as another strange and unpredictable aspect of the vampire world and it could potentially change their relationship with the Cullens. Jacob, in particular, would probably be very confused about Bella's new situation.
There could be Edward. Even though the focus is on Carlisle and Bella, Edward's presence might still be felt as he was an important part of Bella's life before. His reactions to Carlisle and Bella's relationship could add some drama.
At first, it would be a bit awkward as Bella adjusts to her new life. But Carlisle would be very patient and understanding, like a father figure. Esme would be more of a motherly presence, always there to comfort Bella. As time goes on, they would become closer. Carlisle might teach Bella about the vampire history and ethics, and Esme would share her love for the family and home. Eventually, they would have a very strong, loving bond.
If Bella was Carlisle's daughter, her relationship with the other Cullen siblings would be altered. She would be part of the family in a more fundamental way. For example, Alice might see her more as a sister to protect and guide, rather than just a friend. And Rosalie might have a different attitude towards her, perhaps being more accepting since she is Carlisle's daughter. Jasper could also be more involved in her training or development as a vampire, as he has his own skills and experiences to share.
Well, in fanfiction, anything can happen. Since it's not bound by the strict canon of the Twilight series. It could be that the writer decided to create a completely different timeline or scenario where Carlisle and Bella have a relationship that leads to her pregnancy. It might involve some kind of genetic manipulation or a special power that allows for this unorthodox union to result in a pregnancy.
In these fanfictions, Carlisle could develop by becoming more involved in the family on an emotional level. He's always been a bit reserved, but the pregnancy could break down some of those walls. Esme might grow in confidence as she realizes she's bringing new life into the family. She could also become more assertive in protecting the unborn child, which is a new side to her character. As they go through this journey together, their bond as a couple could strengthen, and they might start to understand each other in ways they hadn't before.