Вот здесь есть обсуждение по этому поводу:
https://scifi.stackexchange.com/questions/197708/why-are-the-weasleys-specifically-considered-blood-traitors

В каноне предателями крови называют:
- Вальбурга - Сириуса
“Yoooou!’ she howled, her eyes popping at the sight of the man. ‘Blood traitor, abomination, shame of my flesh!”
- Отец Меропы Гаунт - Меропу
"You disgusting little Squib, you filthy little blood traitor!" roared Gaunt, losing control, and his hands closed around his daughter's throat.
- Слизеринец Гарпер - Рона
"Thinks he's something special today, doesn't he?" said a snide voice, and Harry was nearly knocked off his broom as Harper collided with him hard and deliberately. "Your blood traitor pal..."
- Забини - Джинни
"I wouldn't touch a filthy little blood traitor like her whatever she looked like," said Zabini coldly, and Pansy looked pleased.
- министр Тикнесс - Артура
"Ah, well. It's only a matter of time," said Thicknesse. "If you ask me, the blood traitors are as bad as the Mudbloods. Good day, Runcorn."
- Фенрир Сивый - каких-то Уизли
"A Weasley?" rasped Greyback. So you're related to blood traitors even if you're not a Mudblood.
- Беллатрикс - Рона
"If she dies under questioning, I'll take you next," she said. "Blood traitor is next to Mudblood in my book.
- Сириус - семью Уизли
But there's no point looking for them on here — if ever a family was a bunch of blood traitors it's the Weasleys.
- Рон - свою семью
"My whole family are blood traitors! That's as bad as Muggle-borns to Death Eaters!"
"It was always a matter of time, Dad's been saying so for months. We're the biggest blood traitor family there is."