what if the reason nobody can tell fred and george apart is because they really are interchangeable
not in a ~it doesn’t matter~ way but like. molly and arthur used to worry that fred and george might turn out to be squibs because they weren’t doing any accidental magic as children, but they were, THEY TOTALLY WERE, it just wasn’t anything flashy, instead they were just like idly switching bodies all the time
and like sometimes it doesn’t make much of a difference, whatever, wake up in the opposite bed you went to sleep in, but it gets like dangerous and weird if you’re on a broom or in the pond or letting your mum teach you to cook or trying to be mad stealth, so for a long long time everybody presumes they’re clumsy maybe-squibs and that they’re doing their twin lying thing when they try to explain what’s going on, so they learn to handle the issue their ownselves
they just. don’t go anywhere without the other. they start each day deciding which body is going to be which (because at this point they really don’t know which body is technically fred and which is technically george), and they learn to reorient FAST when they switch, and what things set them off, and eventually they learn how to act like nothing’s up even when one of them’s in the air and one’s on the ground or whatever, and then they burn past that til they can finish each other’s sentences — til they can switch midsentence — til they can play beater together — til they can switch in a split second in the middle of a game — til there’s room for other kinds of accidental magic to start showing up
at hogwarts they keep each other awake in history of magic by switching back and forth. in potions they take turns brewing and keeping lookout for the slytherins. in transfiguration and charms they keep their grades up because one of them will always get a spell right on the first try so they switch and make it look like both of them do and then they practice on their own later in private. it keeps the mystery alive.
at first they thought lee was just a lucky guesser but no, lee can always tell one twin from another twin — it’s not exactly telling fred from george, because while they are definitely two distinct personalities neither one of them feels like fred all the time or george all the time — but lee knows who he argued with yesterday or who he lent his notes to or who’s best to ask for help in astronomy and who’s best at runes.
the weasleys are pretty bad at it for the longest time, but then bill comes home from his first year cursebreaking and he can tell, and over a holiday he teaches his trick to charlie so charlie can tell. alicia and katie and angelina can tell. the twins honestly don’t know if oliver can tell or not; so long as they’re doing what they’re supposed to on the quidditch pitch he doesn’t really care about much else. harry can tell. luna can tell. tonks can tell.
the problem is there’s no way for this to end happily