It could be Iron Man. Since he was always the brains behind a lot of the Avengers' tech and strategies, he might be the one analyzing every detail in the trailer and coming up with plans.
Captain America could be the main focus. He represents the moral compass of the Avengers. In this fanfiction, he might be the one guiding the discussion on whether they should interfere in the events shown in the trailer or not. He would consider the greater good and how their actions could affect the balance of the multiverse. For instance, he might be concerned about protecting the innocent people who could be caught in the crossfire of the battles between the returning villains and the heroes in the No Way Home movie. Also, his leadership skills would come into play as he tries to keep the Avengers united in their views regarding the trailer.
I think it could be Clint. He has a family and the thought of his family being Snapped away would be devastating. He would be haunted by the idea that he wasn't there to protect them. He might feel a great sense of guilt and loss compared to the others.
In this fanfiction, perhaps the Avengers are watching the trailer together in the Avengers compound. They might start arguing about whether the events in the trailer are going to be good or bad for their world. Some could be excited to see old foes return, thinking it's a chance to set things right, while others might be worried about the chaos it could bring to the already fragile multiverse. For example, Iron Man could be analyzing the technology shown in the trailer, trying to figure out if it's something they can use or need to defend against.
There's a fanfiction where the Avengers watch 'No Way Home' and it really focuses on how Doctor Strange's actions in the movie inspire Wanda Maximoff to further explore her powers. She sees how Strange manipulates the multiverse and starts to think about how she could do something similar with her chaos magic. It's a great read for seeing Wanda's character grow in new ways.
Captain America is also a key focus. His leadership qualities are highlighted. He could be seen rallying the other Avengers as they watch the trailer, giving inspiring speeches about not giving up and fighting for the universe.
Black Widow could be a great focus. Despite her sacrifice, in fanfiction, she could have left behind some crucial information or skills that the remaining Avengers use in 'Far From Home'. Maybe she had some knowledge about the type of technology Mysterio is using or some combat techniques that are useful against his illusions. Her backstory and her relationships with the other Avengers could also add depth to the story.
There's a fanfiction where the Avengers watch the trailer and then start making bets on what will actually happen in the movie. It's a really fun take on it. The banter between the characters is great, especially between Sam and Bucky. It's called 'Trailer Predictions: Avengers Edition' and can be found on Archive of Our Own.
Imagine the Avengers reading 'No Way Home' fanfiction. Loki would probably find it amusing and start plotting his own fanfiction - like twists in his head. Wanda Maximoff might be a bit emotional about it, relating to the characters' feelings in the story. Vision, on the other hand, would be trying to understand the concept of fanfiction itself and then make logical deductions about the Avengers' reactions based on their personalities.
Well, if the Avengers are watching 'Spider - Man: No Way Home' fanfiction, they might be looking for inspiration. Maybe they want to learn from the different scenarios presented in the fanfiction to better prepare for future threats in their own world. They could also be amused by the wild ideas and crossovers that often appear in fanfiction.
Ant - Man would be a likely candidate as his power already involves size - changing. In fanfiction, his ability could be enhanced or malfunction, leading to all kinds of interesting scenarios. For example, he could accidentally make all the other Avengers the same size as him, creating a whole new dynamic for the team.
Some of them might be really amused. For example, Thor would probably laugh heartily at any creative interpretations of his character. He might say 'This Midgardian has a wild imagination!'.