Carlisle, being the peace - loving and rational leader of the Cullens, would first try to understand Jasper's motives. He would probably try to communicate with Jasper to find out why he has kidnapped Bella and see if there is a way to resolve the situation peacefully.
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.
Their friends might be initially shocked. Some, like Alice, might be excited and start planning for the baby's future right away. Others, like Edward, could be more worried about the potential risks to Bella's life.
The Cullens might be shocked at first. If Bella's secret is something really unexpected like she has a hidden power, they will need some time to process it. They could be initially speechless.
Bella could also be surprisingly calm. If she has developed a deep understanding of the vampire world and Jasper's character over time, she might believe that there is a reason behind his actions. She may wait patiently for him to explain himself while also observing her surroundings for any possible means of escape or self - defense.
Another idea is that the fanfiction could be a dark, alternate universe story where Jasper has turned evil. His reasons for kidnapping Bella could be tied to some sort of revenge plot against the Cullens. He might hold a grudge against them for something that happened in the past, and Bella is just a means to get back at them. This would create a very different dynamic compared to the original Twilight story.
At first, Bella might be shocked and resistant. She could be filled with a sense of disbelief that such a thing is being forced upon her. After all, in the Twilight universe, Bella has her own feelings and desires, especially when it comes to relationships. Forced marriage goes against her free - willed nature. So, she would probably try to find a way to oppose it, perhaps by seeking help from her friends or looking for a loophole in whatever is forcing this marriage upon her.
They might be intrigued. The future in fanfiction could be full of new concepts and relationships that they haven't considered before.
They would probably be intrigued. It's a different take on their own story.
Edward might be initially shocked and heartbroken. He has been in love with Bella for a long time, so her leaving for Jasper would be a huge blow. He could become withdrawn and moody, brooding over what went wrong.
In this fanfiction, they have a very close family - like relationship. The Cullens are like a big family, and Alice and Jasper are important members of it. They care for each other deeply.