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.
The portraits could also show Harry the mistakes and triumphs of his family. He might see that his family wasn't perfect, and this could make him more accepting of his own flaws. At the same time, seeing their great deeds could inspire him to strive for more in his own life, to live up to the family name in a positive way, thus changing his view of what he can achieve and who he is.
It could have a huge impact. Maybe it gives him a stronger connection to his past and helps him deal with his insecurities.
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.
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.
His relationship with the Dursleys would surely become more strained. He would no longer tolerate their mistreatment and might even use magic to protect himself from them if they try to continue the abuse. With his friends, it could bring them closer. Hermione and Ron would be more protective of him and would try to cheer him up when he has moments of self - doubt due to the abuse he's endured.
One possible storyline could be that Harry discovers a hidden room filled with family portraits. As he looks at them, the portraits start to come to life and tell him stories about his family's past that he never knew. Maybe they reveal secrets about his parents' time at Hogwarts or their early relationship.
His idea of family could be more complex. Since he has no real family in the orphanage, he might not have the traditional concept of family. When he finally discovers his wizarding family, he could have a hard time adjusting to the idea of having relatives and a family history.
It completely flips the usual narrative. In the original story, Harry has a sense of longing for his family, especially his parents. But in this fanfiction, the hatred changes the emotional core. It makes Harry a more complex and perhaps darker character. The relationships that were once sources of strength, like his connection to his parents through their sacrifices, now become sources of bitterness.
The portraits can act as a source of emotional support. Just seeing their faces and the expressions of love and pride on them can boost Harry's confidence. For example, when he's feeling down about his latest encounter with Voldemort, a glance at their portraits might give him the strength to keep going.
Well, if Snape were Harry's dad in this fanfiction, Harry's isolation might take on a different tone. He could be more conflicted. Knowing Snape is his father, a man he had such a tumultuous relationship with before, would make him question his own identity. He might be more withdrawn as he tries to come to terms with this new family truth, and his relationships with his friends might become strained as he feels they couldn't possibly understand what he's going through.
His perception might become more positive. If he discovers great deeds his family has done in the past, he could feel a new sense of pride.