I wish I could remember the exact regulations about halfbloods and familiars.

My family DEFINITELY couldn't keep them. I wish I could remember if there's an explicit exception made for halfbloods in fostering or if they're just not enforcing the rules on Finnigan because his foster father is important. I can look it up tomorrow in the library but the Ministry's book of regulations for halfbloods and blood-traitor families is not the sort of thing that gets left lying around in Slytherin House.