It could be Michael. Since they have a complex relationship in the Roswell series, it's possible that their relationship takes a new turn and he is the father. Maybe they had a passionate night together that led to the pregnancy.
There's also a chance that it could be a new character introduced in the fanfiction. This new character could be from out of town, or maybe even an alien in disguise who sweeps Maria off her feet and is the father of her unborn child.
Perhaps it's Max. He has always been there for Maria in some ways, and an unexpected moment of closeness between them could result in him being the father. He is also a central character in the Roswell story, so this would add a whole new layer of drama to the fanfiction.
One possible plot twist could be that the father of Maria's baby is not who she initially thought. Maybe there was some sort of mix - up at a fertility clinic or she was deceived by someone she trusted. Another twist could be that Maria discovers she has some sort of alien - related pregnancy, given the Roswell theme, which could bring in all sorts of strange powers or abilities for the unborn child. A third twist might be that Maria decides to keep the pregnancy a secret from most of the people in Roswell, but as she tries to hide it, she gets into all sorts of comical and tense situations.
It could be a long - time boyfriend that we haven't known much about in the original story. Maybe he's a character who was in the background but now becomes central to the plot.
It could be one of her close friends from the guild. Maybe Jellal, considering their complex relationship in the original story. There's already a lot of history between them, and this could be a new development in their relationship.
There's also a chance that it could be a god in disguise. Gods have been known to have relationships with mortals and demigods. So perhaps a god took on a human form and had a relationship with Thalia, resulting in the pregnancy.
It could be her existing partner from the original story. For example, if it's a story where she's in a relationship with Edward, then he would be the likely father.
For Michael's family, if they have been in hiding or trying to keep a low profile in Roswell, the pregnancy could be a big threat to their secrecy. They might be hesitant to get involved for fear of attracting unwanted attention. Maria's family, being human, might have a hard time adjusting to the idea of having an alien - related pregnancy in the family. They could initially be resistant, but over time, with understanding and seeing Michael and Maria's commitment, they might come around.
A possible plot could be that there's something special about the baby because of their alien heritage. Maybe the pregnancy progresses differently compared to a normal human pregnancy. They could discover that the baby has unique powers or abilities that start to show even before it's born. This would add an element of mystery and danger as they try to protect the unborn child from those who might want to use its powers for their own gain.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of Roswell fanfictions, including many about Michael and Maria. Another place is FanFiction.net. There are also some Roswell - focused fan communities on social media platforms like Tumblr, where users might share or recommend good Michael and Maria fanfictions.
One great michael and maria roswell fanfiction is 'The Unseen Bond'. It delves deep into their relationship, exploring how they deal with the challenges in Roswell. Another is 'Michael's Hidden Feelings' which focuses on Michael's inner thoughts regarding Maria. And 'Maria's Discovery' shows Maria finding out new aspects about Michael that she hadn't known before.
Another option could be a mysterious figure. For example, a character from another dimension or a new character introduced specifically for this plot twist. This could add an element of mystery and intrigue to the story.