IIRC it something like Fubuki hired as Gen 1 -> Holo makes Gamers group* -> Mio recruited due to Fubuki suggestion/referral** as part of Gamers** -> Okayu got scouted, but still had to pass an audition -> Korone came in as a package deal with Okayu -> Hololive had a bit of restructuring (can't remember exactly when) and now they're all the variety streamers we know.

* Back then they were all general streamers and the odd bit of singing.

** Can't remember exact phrasing used, but Fubuki suggested Mio audition, but Mio didn't reveal her relationship with Fubuki until after she was accepted.

***This was a few months post Gen 2 but Gen 3 was way off yet, so Gamers was a way for Mio to be part of a group instead of a lone talent. Sort of how IrYS's lore ties her to Council, rather being completely on her own.