Well, Bella would probably have a very strong emotional reaction. Given her character, she would likely withdraw into herself at first. She might start to question a lot of things, like the safety of the world around her. Her relationships with others would also be affected. For example, she might push away those who try to comfort her because she's so consumed by grief.
She might be devastated. Bella could go into a state of shock initially. Then, she might feel a deep sense of loss and loneliness. She could also be filled with anger towards the cause of her father's death.
It could be an old enemy of Bella's family. Maybe someone who had a grudge against her dad from his past.
Well, it could lead to all sorts of drama and emotional turmoil. Maybe Damon offers her comfort or protection.
Yes, there are some. You can start by looking on popular fanfiction websites like Archive of Our Own or FanFiction.net. Just search for the specific tag 'Edward is Bella's step dad' and you'll find various stories with different takes on this rather unique concept.
One possible plotline could be Bella initially resenting Edward as her step - dad but then gradually coming to understand him better and they form a unique bond. Another could be Edward struggling with his new role and having to deal with his own feelings for Bella in a more platonic way than in the original story.
She could be heartbroken. After all, she's pregnant and the person she loves has left her. She might feel abandoned and alone, crying a lot and wondering why Edward would do such a thing.
Often, Bella reacts with intense heartbreak. She might isolate herself from her friends and family, feeling like she can't trust anyone anymore after Edward's betrayal.
Bella might initially be terrified. She is a human being kidnapped by a vampire, after all. She could struggle and try to escape, using her wits and any available resources. However, since she has feelings for Edward in the original story, part of her might also be conflicted, wondering if there is a good reason behind his actions.
She might feel a sense of comfort. Since Carlisle is an authoritative and kind figure, his gesture could make Bella feel safe.
His dad might be initially shocked but quickly become accepting. After all, he is a god and has seen many strange things. He would probably use his power to make Percy's life easier during the transition, like providing resources or protection.
He might be very empathetic. He could offer her a safe space and listen intently. Maybe he'll use his calm and understanding nature to make Bella feel supported.