когда умерли его родители?
1977 от какой-то магической болезни. Допы Роулинг.

драконья оспа, не?

А вот это ХЗ.
Mother: Died between 1978 and 1981. She was elderly, even by wizarding standards, and died from a wizarding illness. There is “nothing sinister” about her death (TLC).
Father: Died between 1978 and 1981. He was elderly, even by wizarding standards, and died from a wizarding illness. There is “nothing sinister” about his death (TLC).
Да, с датой немного промахнулась.