They might be really excited, especially if the fanfiction contains interesting new storylines or character developments that they haven't thought of before.
Maybe it's for a school project on modern pop - culture and fan - created works. They could be analyzing how fanfiction adds to the Endgame story and its impact on the fandom.
Some students in Peter's class might be really excited as they get to see new takes on their favorite movie. Others could be a bit confused if the fanfiction is very different from the original story.
He might raise an eyebrow in surprise at some of the more out - there plot twists in the fanfiction.
Peter would probably be shocked at first. I mean, getting a call from Deadpool in the middle of class is not an everyday occurrence. He might quickly look around to see if anyone noticed his phone ringing.
In many fanfictions, Howard Stark is often portrayed as being deeply moved and intrigued by the events of Endgame.
Perhaps Peter is a bit annoyed at first. He's trying to focus on class and here's Tony calling. But then when he realizes it might be something important, he starts to pay more attention to the call, all while being cautious not to get caught by the teacher.
Peter could also be a bit annoyed if it's not a good time. For example, if he was really focused on a test or a lesson he was interested in. But still, he'd probably answer because he knows Natasha wouldn't call without a good reason. He might give her a look that says 'this better be important' while trying to listen to what she has to say.
It enhances the viewing experience by building more excitement. You get to read all these different takes on what the trailer might mean for the movie, and it makes you more eager to see how the real movie plays out.
Peter Parker might develop by becoming more of a leader. In the fanfiction, he could step up and take charge in certain situations, guiding the other heroes. This would be a big change from his more inexperienced self in the movies.
She could be critical. Given her high standards, she might analyze the plot, the characterization, and the grammar in the fanfiction. If there are inaccuracies in the portrayal of the demigods or their relationships, she might be a bit disappointed.