The older members of Fairy Tail, like Makarov, would likely be very cautious. He has the responsibility of protecting the guild and its members. So, he would keep a close eye on Minerva. The younger members might be a bit more star - struck at first, seeing her as a powerful mage. But as they interact more, their reactions would depend on how Minerva behaves. If she's kind and helpful, they'll accept her, but if she shows any signs of her old ways, there would be problems.
Most of the Fairy Tail members would not take it well. Happy, Natsu's closest friend, would be extremely confused and sad. He'd follow Natsu around, trying to get him to come back to the guild. Makarov, the guild master, would see it as a huge threat to the guild's safety. He might send some of the stronger members to keep an eye on Natsu and Zeref. And the younger members like Wendy would look up to Natsu so much that they'd be very disappointed and scared for him, thinking that he's making a big mistake by joining Zeref.
Well, first of all, Natsu would probably be excited to see himself in all kinds of wild adventures in the fanfiction. He loves action and if the fanfic has him in some epic battles, he'd be all for it. Lucy might be a bit more critical. She'd look at how she's portrayed in terms of her intelligence and her relationships with the other guild members. Gray would likely be cool about it, but might get a bit annoyed if the fanfic made him seem too cold or too goofy. And Erza would be very strict in her assessment. If the fanfic doesn't adhere to the values of the guild she holds so dear, she might not be too happy about it.
Some members might be initially cautious. Given her past as a powerful and somewhat feared being, they would be worried about her true intentions. For example, Gray might be on guard until he sees her actions are genuine.
Some of the more mischievous guild members like Gray might tease them a lot. He'd probably make jokes about it every chance he gets, much to Natsu and Lucy's annoyance. Happy, on the other hand, might be really confused at first but then start to see it as a sign of their closeness and be really happy for them.
Fairy Tail would be a mix of reactions. The younger members would be thrilled and look up to Naruto as a hero. The older and more experienced members would assess his skills and how he could fit into the guild. They might also be a bit protective of their way of life in the guild at first, but as they get to know Naruto better, they would accept him as one of their own.
Their interaction could be quite interesting. Minerva might initially be dismissive of Lily, seeing him as just another member of Fairy Tail. But as time goes on, she realizes that he has a depth of character that she hadn't expected. For example, Lily could show great courage in a battle, which earns Minerva's respect.
She could be a powerful addition to the guild. Maybe she starts off as a bit of an outcast due to her past actions in Tartaros. But as she spends more time in Fairy Tail, she gradually warms up to the others. She might use her strong magic to help the guild in battles against new enemies, like some dark guilds or other threats that emerge. And perhaps she forms new friendships, especially with those in Fairy Tail who are also strong magic users.
Some members might be sad at first. Lucy, for example, would surely miss him a great deal as they are close friends. She might worry about him constantly during his absence.
Goku would probably get along well with Natsu. They both have a love for fighting and a strong sense of justice. They might constantly challenge each other to friendly battles to see who's stronger.
Drunk Lucy could also be very argumentative. She might start debates with the more serious guild members like Erza about the silliest things, like whether or not it's proper to eat cake with a fork or hands. This would lead to some comical exchanges as the other members watch in amusement.