In the fanfic, it could be that Snape is caught in a political struggle within the wizarding world. Harry, who is on the side of the 'good' political faction, uncovers Snape's involvement in some underhanded schemes for the opposing side. As a result, he has no choice but to get Snape arrested to protect the safety and stability of the wizarding community.
Dumbledore would be a key figure in the reactions. If he believed in Snape's innocence, he would try to find a way to free Snape while also not alienating Harry. He might start his own investigation to uncover the truth. The other Hogwarts teachers would be in shock. Some might believe Harry is right, especially those who have always been a bit suspicious of Snape, while others would be outraged and demand an explanation from Harry.
Maybe Harry accidentally frames Weasley for something. It could be due to a misunderstanding, like a spell gone wrong that makes it seem like Weasley was involved in some illegal magic use.
One possible plot could be that they discover they are brothers early on in Harry's time at Hogwarts. Snape then has to balance his duties as a teacher and his newfound family connection. He tries to protect Harry in secret from the threats within the school, like Malfoy and his cronies.
Perhaps in the fanfic, there is some sort of magic that binds their fates together. Snape might discover this connection and, despite their past differences and his own reserved nature, he decides to propose to Harry as a way to accept this newfound bond. It could also involve Snape trying to make amends for his past actions towards Harry by offering this ultimate commitment.
One possibility could be that Dumbledore arranges for Harry to live with Snape for protection. Snape, though reluctant at first, gradually discovers Harry's hidden strengths and they form an unlikely bond. Harry might learn more about his mother from Snape, which could lead to a deeper understanding between them.
Well, it could be that Snape has some false information that makes him think Harry is in immediate danger from the wrong people at Hogwarts. So, he kidnaps Harry to protect him. Maybe he takes Harry to a secret location like an old, abandoned wizarding house in the Forbidden Forest. There, he tries to figure out what to do next while Harry is really confused and angry at being kidnapped.
I'm not sure of a specific fanfic on this topic, but you could try searching on fanfic platforms like Archive of Our Own. Use the tags 'Harry Potter', 'Severus Snape', and'mpreg' to narrow down your search.
One possible plot could be that Snape, seeing the troubled situations of both Harry and Draco, decides to take them under his wing. He could start by teaching them more advanced magic in a strict but fair way. Harry might initially be resistant as he has his own ideas about Snape, but gradually realizes Snape's good intentions. Draco, on the other hand, might struggle with the idea of being under Snape's authority as he is used to his family's influence. They could all learn to live together, with Snape guiding them through the challenges of Hogwarts and the wizarding world at large.
Well, it could be that Snape is wrongly accused of a great crime in this fanfic, and in the heat of the moment, someone attempts to kill him. Maybe it's a misdirected act of revenge by someone who thinks Snape is behind a series of dark events at Hogwarts. But of course, the truth might be far more complex and intertwined with the overall politics and secrets of the wizarding world.
One possible plot could be that Snape, out of a sense of guilt or a newfound understanding of Harry's situation, decides to take him in. Snape would have to deal with Harry's grief over his parents and his own complex feelings towards the boy. He might start to teach Harry magic in a more personal and different way than at Hogwarts, leading to a unique bond between them.