When petunia heard the news of her sisters passing, she took it harder than in canon.

She started to drink heavily, and get depressed. Petunia hid what little love she had left for lily pretty good, so it destroys her when she hears of what happened.

Vernon doesn't know what to do when his wife becomes a distant drunk, so he ends up raising both his son and harry to the point where he treats harry like a second son.

Dudley knows that he is supposed to love his mother, but can't seem to care much for someone who was barely in his life. Although he does appreciate when she gets a rare bout of lucidity.

Harry upon learning that potions can do pretty much anything from Snape during his first potions class, he dives head first into his potions textbook, and it shows in his grades. He is determined to help his aunt return to how she once was, if only to return the kindness his uncle and cousin shown him over the years.