I came late to the HP fandom and have seriously overdosed on remus/sirius fic since December. You are right about the different interpretations of Lupin's parents. Canon seems to determine James and Sirius' parents but I was quite surprised that there is no fanon consensus about Remus' (or Peter's!) parents, as sometimes happens (and has happened for other aspects, such as Remus' love of chocolate or Sirius dating a lot of girls).