(Updated) Where do these characters originate

Yes, John Doe, Noli, and 1x are real accounts, so myths can be both real or fake accounts, like guest 666 for example, he's not a real accounts. Also, yes, Mafioso is from Dream Game, but this version is the forsaken version and not the original version.

I know that 1x and John Doe are real accounts

and you forgot Jason. (Now as Slasher)