They might be worried about Tony Stark's mental state. In 'Iron Man 3', Tony is clearly dealing with a lot of post - trauma issues from the events in New York. The Avengers, who know him well, would be on edge seeing him struggle like that.
Well, they could be quite impressed with how Tony manages to handle the villains on his own most of the time. He's resourceful and uses his intelligence to get out of tough situations. In the fanfic, the Avengers might be cheering him on silently or even having a bit of friendly competition among themselves to see who could have done better.
They might be amused. The Avengers know Tony Stark well, and seeing different interpretations of his character in the Iron Man 2 fanfic could bring out some laughter. They may also be critical in a friendly way, like pointing out things that are not in line with what they know about Stark or the events in Iron Man 2.
In fanfiction, the Avengers could have a range of reactions. Hulk might not care much about the drama but be more interested in the destruction. Black Widow would probably be analyzing every move, looking for any weaknesses in the villains' plans. Captain America could be feeling a bit out of place with all the modern technology. And Iron Man himself? The others might be in awe of his ability to keep going despite all the odds against him in the movie.
The Avengers could be intrigued. They might see some similarities between Moon Knight's fight against evil in the fanfic and their own battles. Captain America, for example, would probably admire Moon Knight's determination in the face of danger, even if he doesn't fully understand all the Egyptian mythology stuff that's often part of Moon Knight's story. Thor might be interested in any connections to the otherworldly elements in the fanfic, comparing them to his Asgardian knowledge.
They might be quite amused. For example, Thor could find the strange and magical elements in the fanfic similar to his own Asgardian adventures. He might laugh out loud at some over - the - top magical stunts described in the fanfic.
They would probably have a lot of banter. Tony would be making snarky comments about his own actions in the movie, and Steve would roll his eyes at some of his more egotistical moments. Thor might be sharing his thoughts on the magic - like technology, which would be really interesting. Natasha and Clint would be sharing knowing looks during the more intense scenes.
Maybe Vision. Since he's more about facts and logic, he might find fanfic a bit too fictional and not based on real events. He could struggle to understand the point of it when it deviates too much from what actually happened.
They might be surprised at how their actions are reimagined. For example, Iron Man could be astounded to see a version of himself in a situation he never thought of in the official storylines.
They might be really surprised. The Avengers are used to their own set of adventures, and this fanfiction about 'The Impossible' would show them in a whole new scenario that they may not have expected. It could be both exciting and a bit strange for them to see this new take on their characters.
They might think it's quite imaginative. The Avengers are used to dealing with real - life superhero situations, but the fanfiction could present scenarios they've never considered.
They might be proud of Spider - Man. He has grown a lot and is handling big responsibilities well in the movie.