Is there anything different about Sans and/or Papyrus in this AU?
(Sorry for the late reply, I only just saw this TwT)
I don't think there would be major differences? I'm not really sure
I don't think Toriel and Sans are as close as they are in the game. Toriel doesn't have time to tell jokes at the door when Copper pops up. BUT she does tell him about Copper, under sworn secrecy, so I imagine Sans becomes a little bit more human friendly. Something to note is that he never holds Copper to judgement - it's always just Frisk. In the genocide route, Copper's talking to Asgore while Sans is 'talking' to Frisk. This is true for most routes, actually, so I like to imagine Toriel tells Sans about Copper in their minimal joke-tellings, and so he trusts that kid more.
But I think Papyrus would remain mostly the same. This might change later on, of course, but I don't see him changing much?
I want this to be focused mainly on the Human Bros rather than the Skeleton Bros (ha) bUT I am open to suggestions about them!!!!! And any other character!!!! Please feel free to give. Ideas. :)