The other Cullens like Carlisle and Esme are bound to be part of the story. Carlisle, as the family's patriarch and a doctor, would be involved in Alice's medical care during the pregnancy. Esme, with her motherly nature, would likely be there to offer emotional support and help prepare for the new arrival.
Edward would be a likely character. As part of the Cullen family, he would have an interest in Alice's situation. He might offer his support or advice based on his own experiences in the Twilight world.
Hal could be a very likely character. Since he was Alice's husband in the show, he could play a big role in the fanfiction. He might be the father, or he could be dealing with the news in different ways, like being supportive or having doubts. Another character could be Betty. As Alice's daughter, she would surely be affected by her mother's pregnancy. She could be helping Alice out or having her own emotional turmoil because of it.
The Cullens are often involved too. Edward, for example, as Alice is part of the Cullen family. Their interactions can be explored in different ways in fanfic, perhaps showing a different side of their family dynamic.
Perhaps the story focuses on how her pregnancy affects her special abilities. Since she can see the future, will she be able to see the future of her unborn child? And how does that knowledge or lack of it impact her decisions during the pregnancy.
Well, there could be a little mouse. Since Alice is shrunk, the mouse could be her guide in this new, small world. It might show her where to find food or shelter.
Well, Naruto himself could be involved. He might be concerned about Tsunade's pregnancy and offer his support in some way, like running errands for her or helping to keep the village in order while she's dealing with her pregnancy.
A common theme is the exploration of a mysterious twilight world. Alice often ventures into this unknown realm, filled with strange creatures and phenomena. Another theme is self - discovery. As Alice faces the challenges in the twilight setting, she learns more about herself.
In Twilight fanfiction, if Bella were pregnant by Alice, it would completely shatter the existing relationship dynamics. First, it goes against the canon relationships in the series. However, in fanfiction, it could lead to a whole new exploration of the characters. Maybe the Cullens would be divided in their reactions. Some might be accepting, while others could be horrified. It would also change Bella's relationship with Edward, as this would be a huge deviation from their story. And Alice herself would have to deal with unexpected motherhood, which could change her carefree and prescient nature.
Definitely Alice, as she is at the core of any 'Alice in Wonderland' - based story. The Caterpillar could be another important character in this kind of fanfic. The Caterpillar, which is already a symbol of transformation in the original story, could have a more complex role as it observes Alice's slow shrinking. Maybe it could offer some sort of guidance or be a source of knowledge for Alice as she deals with her changing size in this new version of the story.
I'm not a huge fan of lemon fanfics in general, but if it's about Alice and Jasper from Twilight, it could be really interesting. Maybe it focuses on their relationship in a more steamy or different way than in the original books. It might explore some uncharted aspects of their love story.
One interesting concept could be exploring Alice's backstory more deeply in the Twilight universe. Maybe her life before becoming a vampire and how it shaped her abilities.