Mal herself is likely to be a very popular character in such fanfiction, as she is a central figure in the 'Descendants' world. Her story arc can be easily adapted to include a pregnancy plot. Evie might also be involved, either as a friend supporting Mal or having her own related story. Jay could be another character who might play a role, perhaps as a protector or someone with a connection to the events related to the pregnancy.
Definitely Mal is a top character in this type of fanfiction. She has a strong personality and a complex backstory that can be intertwined with a pregnancy storyline. Carlos could also be involved. His friendship with Mal might lead to him being part of the story, like helping her through the difficulties of pregnancy. Uma might also be included in some fanfictions, as she has an interesting relationship with Mal and could add drama to the story of the pregnancy.
Jaune could be a popular character in such fanfictions. If Ruby is in a relationship with him, he would play a major role in the story. He could be shown as being nervous yet excited about becoming a father. Pyrrha might also be involved in some way, perhaps in flashbacks or as a guiding spirit for Jaune, even though she's no longer alive in the main series.
Obviously Clary herself is the central character. Jace is also very often involved as he is Clary's love interest. Alec and Isabelle Lightwood might also play important roles. They could be the ones helping Clary through her pregnancy, giving her advice or protecting her from any threats.
Loki is the main one for sure. His wife, of course. And then there could be other Asgardian characters like Heimdall. Heimdall, with his all - seeing abilities, could play a role in protecting Loki's wife during her pregnancy. There might also be some of Loki's old allies or foes from his past adventures who get involved in the story, either to help or cause trouble.
One possible plot could be that Mal discovers she's pregnant and has to keep it a secret at first. She's worried about how Ben and the people of Auradon will react. As she tries to hide it, she faces challenges like morning sickness during important events.
In this fanfiction concept, Ben and Mal having a baby could bring a whole new dynamic to the Descendants universe. It might show their growth as characters as they prepare to become parents. They would have to deal with the challenges of ruling Auradon while also raising a child. Their friends, like Evie and Jay, could also play important roles in the story, perhaps helping with babysitting or giving parenting advice.
Obviously, Mal is the central character. But often, her friends or romantic partners can be important characters too. For example, if she has a significant other, they will play a big role in how she copes with the pregnancy.
Obviously, Harry himself is the central character. But there could also be appearances by his friends like Hermione and Ron. They might play different roles compared to the original books. For instance, they could be more protective of Harry or have different reactions to his new family connection.
One thing that could be in the fanfiction is the preparation for the baby. They would need to get a nursery ready. Mal might want to incorporate some Isle - of - the - Lost - style elements into the nursery, while Ben would prefer more traditional Auradon decor. And then there's the matter of their relationship. They would need to grow even closer and support each other more as they anticipate the arrival of their child.
FanFiction.net also has 'Descendants' fanfiction. You can use the search bar and type in relevant keywords like 'Mal' and 'pregnant' to find the stories you're interested in. But remember to be cautious as not all stories might be of high quality.
I'm not really into that specific type of fanfiction, but you can try searching on popular fanfiction websites like Archive of Our Own. They usually have a wide variety of stories, and you can filter by the 'Descendants' fandom to find ones related to Mal and pregnancy.