Even if Harry’s grandparents were alive when the story began in earnest, only Mr. and Mrs. Evans would have fallen within the realm of Dumbledore’s spellwork. The reason that Harry stays with the Dursleys, rather than with literally anyone else, is because Petunia Dursley (Fiona Shaw) is related to him by his mother’s blood. In “Harry Potter and the Order of the Phoenix,” Dumbledore explains to Harry how he is protected under their roof by an ancient magic that Lily triggered when she sacrificed herself to protect him from Lord Voldemort (Ralph Fiennes).
“While you can still call home the place where your mother’s blood dwells, there you cannot be touched or harmed by Voldemort. He shed her blood, but it lives on in you and her sister. Her blood became your refuge,” Dumbledore says. “You need return there only once a year, but as long as you can still call it home, there he cannot hurt you. Your aunt knows this … She knows that allowing you houseroom may well have kept you alive for the past fifteen years.”
Dumbledore’s spell, the death of Harry’s grandparents, and the bald-faced villainy of the Dursleys make up J.K. Rowling’s one-two-three-hit combo that ensures her protagonist is isolated and sympathetic, even if it does gloss over reality. It is statistically improbable that every other person who shares some blood connection to Lily is dead, and even more so that everyone related to James is dead, too. However, Muggles didn’t have social media in the 1990s to keep in touch with their loved ones, and the magical community tends to obey Dumbledore’s every whim. As such, Harry’s extended family being dead is a tragically cleaner way to justify the narrative.
