Albus wrote:Ah, Eol, you touched one of the greatest questions...
Nowhere in the books is clearirly written which House they belonged to, anyway we can make some suppositions:
1) Probably they were in the same House, because they were friends, but this is not a proof. A proof may be tha fact that Lupin says in Book 5 that DD chose him as a prefect instead of James or Sirius![]()
2) Harry probably attends his father's House (as Ron is in his parents' and brothers' and Draco in his father's)
3) Phineas Nigellus speaking of the Black family, in Book 5, says "We Slytherin"... So was Sirius in Slytherin... ???
My personal opinion is that they all were in Gryffondor
Albus, your second supposition is a little questionable. Don't forget that if Harry is sorted to his father's house automatically, the Sorting Hat had first chose Slytherin for Harry. Harry chose Gryffindor.
Secondly, I don't think family is a strong criteria for the Sorting Hat. Padil and Padma are sisters and in different houses.
IMHO
John