Stefan might become more protective. His usually brooding nature could turn into a fierce determination to keep his family safe. Caroline, on the other hand, would probably become more nurturing. She was always strong - willed, but now she would focus that on taking care of the baby. She could also become more of a mediator between Stefan and any potential threats to their family.
It could start to develop in new ways. For instance, if they go back to a time when Stefan was still with Elena, Caroline might see a different side of him. This could either make her fall for him more or create some tension between them. But as they work through these issues, they could end up with a deeper and more complex relationship. They might also discover new things about each other that they didn't know before, like hidden fears or desires from their pasts, which would bring them closer together.
There is also 'The Unlikely Bond'. In this fanfiction, it starts with Caroline and Stefan being forced to work together on a school project. Their initial dislike for each other gradually turns into a deep connection as they discover more about themselves through the process.
Love and sacrifice are common themes. Often, one of them has to sacrifice something for the other, like Stefan might sacrifice his safety to protect Caroline. It shows the depth of their love.
I really liked the fanfiction 'Stefan and Caroline: Unlikely Allies'. In this one, they start off as just friends trying to solve a mystery in Mystic Falls. But as they work together, their feelings start to change. It's interesting because it focuses a lot on their personalities and how they complement each other. There are some really good action scenes too, which makes it more exciting.
Archive of Our Own (AO3) is a great place. It has a large collection of fanfictions, and you can easily search for 'Caroline x Stefan' ones. There are different categories and tags to help you narrow down your search.
The theme of 'power couple' is also quite common. Fans like to write about how Caroline and Stefan, with their combined strength, intelligence, and vampire abilities, can take on the various threats in Mystic Falls. They become a force to be reckoned with, and these stories usually have them saving the day in spectacular ways.
There's also 'Caroline's Choice'. This one shows Caroline having to make a difficult decision that involves Stefan. It's a more emotional piece, with great character development. It really makes you feel for both of them as they navigate through the complex situation.
Perhaps in the fanfiction, they go on a honeymoon to a place that has significance to both of them in their past. It could be a place where they first met as vampires or a place that was important in their human lives. Along the way, they encounter other supernatural beings that test their relationship. But their bond as a married couple is strong enough to overcome these obstacles.
One great fanfiction is 'Caroline and Stefan: The Unlikely Bond'. It delves deep into their relationship, exploring how Caroline's determination and Stefan's brooding nature interact. The story has some really intense moments where they face challenges together and their bond grows stronger.