There's a thread on Holo Reddit where they named the Pro VA talents that Marine is working with on this project.
Reddit Hololive: Winning voice actors for Marines game - The Second World
This is an insanely stacked lineup of VAs:
Sefo: Haruki Ishiya
(Jin Mazama in Seton Academy; Rigur in That Time I Got Reincarnated as a Slime; Masato Oosuki in Do You Love Your Mom and Her Two-Hit Multi-Target Attacks?)
Naririsha: Misato Fukuen
(Chibiusa in Sailor Moon; Toga in MHA; Golden Darkness in To Love-ru; Yin in Darker than Black)
Dithereven: Hiroki Touchi
(Abel in Trinity Blood; Baldroy in Black Butler; JP Dub for Dean Winchester in Supernatural; JP Dub Nathan Drake in Uncharted games; JP Dub Chris Redfield in Resident Evil)
Tina: Ayane Sakura
(Uraraka in MHA; Yotsuba in The Quintessential Quintuplets; Mitake Ran in BanG Dream!; Nao in Charlotte; Kokoa in Is the Order a Rabbit?; Shimakaze in KanColle; Epsilon in Overlord; Gabi Braun in AoT; Iroha in My Teen RomCom SNAFU Too!)
Riana: Marina Inoue
(Armin in AoT; Momo Yaoyorozu in MHA; Yoko in Gurren Lagann; Sora in I Don't Have Many Friends; Tooka in Date A Live)
Thor: Seiichirou Yamashita:
(Cid Kagenou in The Eminence in Shadow; Kakeru in Orange)
Guat: Mie Sonozaki
(Arle Nadja in Puyo Puyo Tetris; Shimura Nana in MHA; Viola in One Piece)
Some of the other Seiyuu who auditioned also have parts as narrators and things.
I missed it but apparently Marine had the Holomem auditions and then at the end of that stream said she would be using professional VAs for the project. Which is great but also i think some of the Holomems, ( ahem, AZKI, ahem) were great.
Koefficient was dragged into the VTuber rabbit hole by his chat about two years ago and now has a series he recently started with VTuber guests where he chats with them, plays some games, has some silly quizzes etc. It's been pretty good fun.
The latest guest is Mika from NijiID, if you've watched any NijiEN then you'll have seen Mika as she collabs with them a lot.
There's also a highlight vid in the description.