They could be very protective. After all, Edward is their son. So they might be a bit cold to Bella at first, sizing her up.
One possible reaction is that they are overly friendly right away. They might be so glad that Edward has found someone he loves that they welcome Bella with open arms. However, they could also be reserved and polite but keep their true feelings hidden until they know Bella better. For instance, they may ask her a lot of questions about her family and her life to understand her better.
They could be skeptical. They might wonder if Jaden has good intentions towards Alexis. So they could be a bit cold at first, observing Jaden closely and waiting to see how he behaves. This would put Jaden in a tough spot, having to work hard to win them over.
Draco's father, Lucius, might be very disdainful at first. He has a strong sense of pure - blood superiority and Hermione is a Muggle - born. His mother, Narcissa, might be more reserved in her dislike. She could be more focused on how Hermione's presence affects Draco.
In this kind of fanfiction, there could be a lot of tension. Maybe Bella is really nervous to meet them as she loves Edward. His parents might be initially skeptical of her, but as they get to know her, they start to see why Edward is attracted to her.
He could be shocked. After all, he may have thought his parents were long gone or never expected to meet them.
In some fanfictions, Edward might be initially shocked. He could be worried about Bella's health, considering the unique situation of a human - vampire pregnancy. He might also feel a sense of protectiveness towards Bella and the unborn child, and start making plans to ensure their safety.
He might be completely devastated. In many fanfictions, Edward enters a state of deep despair. He could isolate himself from others, feeling like his world has ended without Bella.
Edward might seek revenge if he believes Bella's death was caused by someone. He would use his vampire abilities to track down the supposed culprit. For example, if he thought a rival vampire or a group of humans were involved, he'd be relentless in his pursuit. His sense of loss would fuel his anger and drive for vengeance.
Jacob might feel extremely angry. In the Twilight series, Jacob has strong feelings for Bella. Seeing her kiss Edward would be like a slap in the face. He could feel betrayed and might even lash out at them.
Bella would likely be very frightened during the car incident. Once Edward saves her, she'd be extremely relieved and probably feel even more attached to him. Edward, on the other hand, would be initially worried and focused on getting Bella to safety. After saving her, he might feel a sense of relief as well, but also a bit of that over - protective feeling that he often has for Bella.
One possible reaction could be shock. Carlisle might be momentarily stunned to see them in an unexpected situation. He could quickly compose himself and offer some words of wisdom or caution. For example, he might remind Edward to be extra careful with Bella considering her human nature.