Honestly just keep writting it like you are writting characters because in a way you are. None of us actually know the cast, we just know our perception of them, their persona if you will. Even if how they present themselves is 100% authentic we still do not actually know them on a personal level so their persona still is on some level a fictional character kind of.
Also AUs are great. Aus are basically the kiddy pool of the RPF fandoms cause it adds that extra obviouse layer of space between you and the actual real person.