so did the beta parents/bros/grandpas whatever have their own session? that’s what confusing me. how did they know what was gonna happen?

Grandpa found the Frog Temple and founded Skaianet, Mom worked for Grandpa, and Dad started investigating about it after two meteors crashed in his neighborhood. Nanna was raised by the Condesce, and even then didn’t seem to know too much about SBURB proper. Bro is the wildcard, where we don’t know much about him, but maybe Lil Cal whispered to him about it? It’s also plausible some of them could perhaps have partial awareness of their Post-Scratch selves through psychic shenanigans.