I have now decided that I’m fully adopting the hc that the entire Black family knew Sirius hadn’t betrayed the Potters but 100% thought he’d killed Peter and those Muggles. I’m also choosing to imagine that there’s a later Order meeting when someone asks Sirius how he’s able to forgive Andromeda for thinking he was a murderer when he’s still slightly icy with the Order for thinking he was the traitor, everyone is eagerly listening in to hear his explanation, only to get hit with “because she at least knew me well enough to know I’d never betray James. She’d met James only once or twice, but she still knew I’d never betray him.” Sirius can get past the murderer belief, especially since he was in fact planning on murdering Peter in POA so it’s not like they were wrong to believe him capable of murder and also he looked bad when he got arrested, but misunderstanding him so badly as to think he’d hand the Potters over to Voldemort? Not so forgivable. Tonks is the only Order member who knew him before he actually likes now (he’s fine with the others that he didn’t know personally as well and of course the kids) since Andy told Tonks what she believed and Tonks, after hearing why her mother thought so, agreed.
I also like to think that the Death Eaters, especially those close to the Blacks, taunt Remus (and some of the other Order members but mostly Remus as Sirius’s old best friend) about this; Remus is dueling Macnair and as Rodolphus fights Kingsley next to him, Rodolphus shouts out something insulting about Remus believing Sirius was the traitor and how Remus clearly never knew Sirius at all, real interesting loyalty Remus has. Bella is “dueling” Sirius (they’re mostly trading non-lethal spells back and forth and talking about what appears to be “darling Cissy’s” 16th birthday party; Kingsley is very confused about what the “Hippogriff incident” is and how it involves the Atlantic Ocean, but Rodolphus emphatically shakes his head and mouths “don’t ask, do not ask” at him so he stifles his curiosity if it can intimidate even a man who endured over a decade in Azkaban) and immediately starts insulting Remus as well, she has literally never gotten past him for believing her cousin to be a traitor, how dare he insult a Black like that. Sirius heaves a long-suffering sigh as he says “Bella, please, calm down” and she doesn’t even look as she waves her hand, stalking toward Remus the entire time like she’s about to tear his head off with one manicured hand, and says “Don’t be silly. Siri, it is my duty as your oldest cousin to defend you, even if you won’t defend yourself. Actually, maybe especially then.” Remus is having a terrible time, and it’s not until about 20 minutes into Bella’s rant about how awful he is that he realizes Macnair has left the room (he also glances around in desperate search of an exit and spots Rabastan in the corner, having not realized what he was walking into and Rodolphus saw him before he could leave again. Sirius is next to him and they’re furiously whispering about something Remus can’t catch. They’re debating about if Bella and Rodolphus would notice if they left, but both tragically believe the answer is yes (they’re right)) (also, Bella’s nails are glittery, similar to Morgan Taylor’s Fame Game shade, only even more sparkly. It is important to me for you to know that. Either she did a spell, she had a House Elf paint her nails, or she found someone willing to give a manicure to an escaped convict, but her nails are painted. It contributes to her intimidation rather than takes away from it. Sirius complimented her on it when they started “fighting” and the Order is really planning on having a talk with him about priorities. Bella thanked him very sincerely) (Bella also immediately called to Rodolphus about “see, my cousin noticed my nails, yet somehow my husband did not.” Kingsley was surprised Rodolphus didn’t give himself a migraine with how hard he rolled his eyes and cautiously went “you good buddy?” Rodolphus quietly said “Freaking Blacks man, the whole family is like this too.” Kingsley nodded but refuses to ask any more questions, he’s heard the stories. Tragically for Kingsley, Rodolphus decided he kind of likes him and passed on that he seems to be a good person to fight when the Blacks are being menaces again, so Kingsley regularly has Death Eaters coming up to fight him and just launching into a rant straight away. Kingsley laments every day that Rodolphus chose him to duel and wishes he’d fought like Jugson or someone)
Tragically for Kingsley, Rodolphus decided he kind of likes him and passed on that he seems to be a good person to fight when the Blacks are being menaces again, so Kingsley regularly has Death Eaters coming up to fight him and just launching into a rant straight away.