Sound Drive apparently produced the BGM for this so it can be assumed that
junya =
Junya Tanaka
Tanatoshi =
Toshihiro Tanaka OR
Toshino Tanabe (did BGM work on the developer's previous game)
shono =
Satoshi Hono
shimizu = probably
Hisayuki Shimizu
Edit: From other games Sound Drive produced music for:
Walkure Romance Series
Sound Director: Osamu Abukawa
Walkure Romanze: Shoujo Kishi Monogatari
Music by: Yuichi "Masa" Nonaka, Jun Kageie, Yuya Saito, Toshino Tanabe
Walkure Romanze More & More
Music by: junya, Tanatoshi, shono, morikawa
Walkure Romanze Re:tell & Re:tell II
Music by: Hono (ほーの), Tanatoshi (タナトシ)
ほーの is a confirmed alias of Satoshi Hono, Toshihiro Tanaka is listed as a songwriter rather than a composer on Sound Drive's website so Tanatoshi must be Toshino Tanabe.