Love your Immortals AU. So Greed and Paninya are in the know that everyone's not human. And Ed, Al, and Winry all know about each other. And considering how casually Greed mentioned it, I'm guessing everyone knows about Ling. But who all is aware of everyone else's species?
So at least in the early parts of this AU here's how things stand in terms of most to least knowledge:
Paninya: friends with Winry/both know what the other is prior to meeting everyone else, after meeting others she fully aware everyone else isn't human from the get go
Greed: knows what ling is and vice versa - Highly suspects the others aren't human but isn't 100% certain, pretty damn confident though
Winry: knows Paninya isn't human but beyond that is unaware of others
Ling: similar to winry, knows greed's not human but beyond that assumes everyone's normal
Ed and Al: know they aren't human (obviously since they're siblings) but otherwise in the dark with everyone else
Mei and Lan Fan: fully convinced they are the only nonhuman present
so pretty much other than greed and paninya everyone's like that meme of the guy at the party going "no one here knows i'm not human", which is utterly hilarious to the two that have some semblance of a clue
eventually some event happens where everyone is revealed more or less all at once, and past that point everyone is up to speed from there on out haha - for the little doodle I posted it's still at the stage where no one knows what ling is greed is just being cheeky to get a rise out of ling's 'definitely normal human' friends