It could have a huge impact. Maybe it gives him a stronger connection to his past and helps him deal with his insecurities.
Well, it might lead Harry to have a deeper understanding of his parents' love for him. It could also inspire him to strive harder to make them proud or provide comfort during tough times.
He would probably be overjoyed. Harry has always longed for a connection with his parents. Getting their portraits would be like getting a part of them back. He might just stand there, staring at the portraits with a big smile on his face, unable to take his eyes off them.
The portraits could offer him emotional support. Just seeing his parents' faces might give Harry the strength to face difficulties. For example, when he's feeling down or facing a tough decision, looking at the portraits could be like getting a warm hug from his parents, even if they're not physically there.
Maybe Dumbledore, if he were still alive in the fanfiction. Dumbledore was highly respected and had a great influence. Knighting Harry would be a way for him to publicly recognize Harry's achievements and heroism on a grand scale.
One way is that Harry discovers a spell that allows him to communicate with the dead. Using this spell, he contacts his parents. They give him advice on how to defeat Voldemort, like a secret weakness of the Dark Lord.
Discovering the family portraits could make Harry feel less alone. He has always felt like an outsider, but seeing his family members in the portraits, hearing their voices and stories, could give him a feeling of being part of something bigger. He might start to think of himself as not just Harry Potter, the boy who lived, but also as a member of a large and important wizarding family with a rich history.
Yes, there might be some extremely dark and out - of - canon fanfictions out there with such a disturbing premise, but it goes against the general nature of the original story where Harry's parents loved him deeply. However, in the vast world of fanfiction, people can create all kinds of strange and often inappropriate scenarios.
Snape could also be a possibility. If Harry did something that Snape considered a serious offense in Potions class, like using an ingredient in the wrong way that could have caused an explosion, Snape might send a howler to scold him. However, it would probably also be filled with his usual sarcasm and dislike for Harry.
On a more magical level, reviving the dead is against the natural order of things in the wizarding world. This could attract unwanted attention from magical authorities or even dark forces. Some might see Harry's act as a dangerous precedent and try to either stop him or use his new - found power for their own evil purposes.
One possible reason could be that he might feel abandoned. Growing up without them, he could resent the fact that they left him an orphan. He might think that if they were really so great, they would have found a way to survive and be there for him.
Lupin could be a likely candidate. Given his experience and his role as a sort of mentor figure to Harry, he could give Harry the talk. It might involve Lupin sharing his own experiences with being a werewolf and how to deal with secrets and prejudices in the wizarding world.