Some sources for these artists:
いでみどり (lyricist) =
Midori Ide
Her
twitter account and
personal blog. Although her reading is given in hiragana as Midori Ide (at least for lyrics works), I have found her
facebook account (related to 歌ネット) with her real name romanized as "Mio Ide".
河原香織 (chorus) =
Kaori Kawahara
Profile and pics of this soprano (ソプラノ) operatic singer.
比嘉誉 (chorus) =
Takashi Higa
His
facebook account (there's no given romanization), but in this
concert brochure his name is romanized as "Takashi Higa". In this huge
pdf file is credited "Higa Takashi" as bass voice for a chorus.
Although the english staff roll of the game gives "Homare Higa" as romanization of this artist, I haven't found a single source that gives a credit to Homare Higa as singer or vocalist, operatic or not. Not always localized credits give correct readings of the artists or staff involved in a game.
金築史朗 (guitarist) =
???
Nothing in the whole internet that gives a clue about this artist romanization, which is quite rare. The staff credits are the only source for the romanization of "Shiro Kanetsuki", which is the most likely reading of 金築史朗.
惇夫 (bassist) =
Atsuo
His
twitter account where there are some photos of some recording with Tenpei Sato.
須藤亜美 (vocal) =
Ami Sudo?
I've got to admit that my romanization source is the
back cover of the NIS America version of the soundtrack.
Anyway, this
twitter account may be her based on the following description (シングアロングソング教), and her displayed name is given as ami_sto, which may suggest that her real name is Ami Suto. Also,
here you can find a profile that says that she gives singing guidance to children and that has performed on concerts and TV Dramas. Not romanization found.