This...this is exactly right
James - the most bisexual who ever bisexualed (could be pan but i like the bi label better)
Remus - gay, can't really see him as bi, probably uses queer as a label tho
Sirius - gay and demisexual, alternatively remussexual / transfem nb or genderfluid
Peter - aroace or unlabeled
Lily - either a lesbian or bi with a heavy preference for women
Mary - that one girl who thought she was straight until she fell in love with a girl (turns out she's bi)
Marlene - lesbian (duh)
Dorcas - lesbian (duh)
Pandora - unlabeled, queer for sure / trans woman
Xenophilius - unlabeled / non-binary
Barty - bi, hooks up with everything that moves
Evan - probably bi, grey/demisexual
Regulus - that's a homosexual if I've ever seen one, bi only for Lily / trans man
Narcissa - (comphet) lesbian
Alice - bi
Frank - 🥁🥁🥁 the token straight !
That's everyone i have a headcanon for i think