There could be family members of the stolen girl as main characters. For example, her parents. They would be the ones most affected by her being stolen and would probably be the ones trying to find her. So, they could play a major role in the story. Also, there might be a detective or someone in a position of authority who is trying to solve the case of the stolen girl.
The stolen girl is likely to be one of the main characters. She is at the center of the story with the title. And perhaps the person who stole her could also be a main character as their actions drive the whole plot.
Maybe there are other characters in the 'other stories' part who are main characters in their respective tales. It could be a lonely traveler who has his own story of struggle and discovery. Or a young artist who is facing some sort of challenge in a big city. Each of these characters in the different stories could be considered main characters in their own right within the collection.
The most obvious main character could be the most beautiful girl in town. She might be the center of some of the stories, with her actions and experiences driving the plot. There could also be other characters like the people in the town who interact with her, such as the local shopkeepers, her friends, or her family members.
Since we don't have the actual book, it's hard to say exactly. But surely the girl in the basement is a main character in that particular story. There could be other characters like the person who put her in the basement or someone who tries to rescue her.
In 'the girl from the sea', the girl herself is surely a main character. There might also be a male character who she has some sort of relationship with.
One possible theme could be loss. The stolen girl herself represents a loss, not just for her family but also in a more general sense of something precious being taken away. Another theme might be survival. Characters in the stories could be in situations where they have to fight to survive, whether it's physically, emotionally or socially.
In the 'stolen day story', the main characters could range from a family member who has their special day ruined, like a mother who planned a family gathering but everything goes wrong and she is the central figure in this 'stolen day' story. It could also be a traveler who is on a journey and has their day stolen by unforeseen circumstances such as missed flights, lost luggage, and getting stuck in an unfamiliar place.
I don't know who the main characters are in this novel as I haven't read it. But they could be people like a detective, the thief, or the victim of the theft.
Lance could be one of the main characters. He could be Pidge's friend who at first underestimates her because she is a girl but then realizes her great potential and becomes her biggest supporter.
There could be a brave adventurer who is searching for the girl when she gets coiled by the Titanoboa. He might be an experienced jungle - explorer with knowledge of the local fauna and flora, and he could be the one to try and rescue her from the snake's coils.
There could be a wise old wizard who guides the little girl in her journey with the dragons. He might have some knowledge about the dragons' powers and how to interact with them.
In addition to the wives and their families, there could be other characters like neighbors or friends. Neighbors might play a role in fueling the conflict or helping to resolve it. For instance, a nosy neighbor could spread rumors that worsen the situation between the wives. Friends, on the other hand, could offer support or advice to the wives during their difficult times, and they might also have their own motives and personalities that influence the overall story.