Rebekah's family has a long history of complex relationships. Her mother, if still around, might see the pregnancy as a way to strengthen their family's position in the supernatural world. However, some of her siblings like Kol might be jealous or feel left out. On Stefan's side, his vampire nature might make his family worry about the implications of having a half - vampire child. They would be concerned about how to raise a child in their world of danger and secrets.
Elena might be a bit shocked at first but then would be very supportive. She would offer her own experiences and advice, even if they are from a human perspective. Bonnie could be worried about the magical implications of a vampire pregnancy and offer to use her magic to keep an eye on the baby's development.
Their friends' reactions would be a mixed bag. Some, like Matt, who is more on the human side of things, would be in awe of this supernatural pregnancy. He'd try to understand it from a human perspective and offer practical help like getting baby supplies from the human world. Meanwhile, the other supernatural friends would have different reactions based on their own agendas. For example, some witches might see Bonnie's pregnancy as a powerful event and either try to use it to their advantage or protect it out of a sense of duty to the witch community. Overall, their friends' reactions would add a lot of drama and support to the fanfiction story.
Elena would likely be angry. She has her own agency and doesn't like being controlled. If Stefan kidnapped her, she would fight back. She might use her knowledge of the supernatural world and her relationships with other characters to try to escape. For example, she could try to call out to Damon telepathically if they have some sort of connection in the story.
Damon might initially be shocked and angry. He has always had feelings for Elena, and seeing Stefan marry both her and Caroline could make him feel betrayed. He might lash out and try to cause trouble for their relationship at first.
Stefan would be extremely worried and angry. As Elena's other love interest, he has a deep connection with her. He would immediately start looking for her, using all his vampire skills and resources. He would probably suspect Damon right away, given their history of rivalry over Elena.
Caroline would probably be really happy. She's always been a big supporter of Stefan and Elena's relationship. She'd be the one planning get - togethers and trying to make sure they have time alone to reconnect.
Caroline would probably be overjoyed and very helpful. She might offer to babysit all the time and give parenting advice based on her own experiences or what she's read. Damon, on the other hand, might be a bit more cynical at first, but eventually grow to love the baby and become very protective.
He could be very protective. Klaus has always seen Caroline as someone special. Now that Stefan is gone, he might feel a stronger urge to keep her safe. He may try to show her that he can be a better option for her than Stefan ever was, not in a mean way, but out of his own feelings for her. He'll likely be very gentle at first, trying not to spook her.
The world would be in shock. The media would be filled with reports of his death. Civilians who had always seen him as a symbol of safety would feel vulnerable. There would be mass mourning in the cities he had protected.