I think about Same Coin way too much.
Especially as a Ford-centric concept.
Like, Ford has not seen or interacted with his brother for over thirty years (save for the portal incident). Even building up to Weirdmageddon, they barely talked. Ford has only the memories of his brother from childhood. He doesn't really know him.
I just imagine that afterwards, as he starts to get to know his brother, things very slowly fall into perspective. Stan will say something or do something that makes him do a double take. And at first he thinks he's just being paranoid. That, because of his trauma, he's seeing Bill everywhere.
But it just keeps happening.
And maybe he thinks that there's something left of Bill inside Stan's head. Something left behind that's causing this, but (to his horror and intense denial) he comes to realize Stan's always been like this. His personality and Bill's have always been eerily similar. He just wasn't there to make the comparison before.
As Ford is grappling (and failing) to understand what it all means, Stan honestly couldn't give two shits. He's just there. Chilling.
I mean, of course he cares that his brother is apparently having some kind of dilemma, but he knows that he's his own person. That Bill is dead and not in his head.
Ford's just traumatized and paranoid.
Eventually, of course, everyone finds out that Bill was Stan's past life and Ford loses his ever loving mind.
I don't think anyone else will react nearly as strongly as Ford. Dipper might get up there, but he might focus in on the whole "reincarnation is real," "if souls are just recycled, what does that mean for individual people," existential parts of the situation. It would bother him a bit that "technically " Bill and Stan are kinda, in a way, the same, but he knows his uncle and knows he isn't Bill.
Mabel is just like, cool, wonder what I was in my past life.
And Stan literally couldn't care less. His mom did past life readings back in the day and that stuff is nonsense to make people feel better about being a nobody in this life. And now that he knows it's real? Doesn't change his opinion. He knows who he is now and that last life mumbojumbo is as important to his self view as his astrology sign. Which is to say, not important in the slightest.
But Ford. Ford's whole world is shattered. He's going to go through it. Every negative emotion known to man is flashing at the same time in this poor man's brain and everyone else just doesn't seem to care!?!?
Having to grapple with finding out just why Stan reminded him so much of Bill. About how he views his brother in the light of this knowledge. Grief and anger and fear and confusion. Emotions that I think will take him a long while to overcome (with the help of his family of course!).
I just love Ford-centric Same Coin, cause, at the end of the day, I really don't think Stan would care too much. It's Ford whose response is the most interesting to me.