Although the OST isn't out yet, there are detailed credits for the music in the game's staff roll sequence.
Not sure if they can already be submitted in this entry or if it's best to wait for the actual CD release.
Anyway, here's the information, taken from the game's credits sequence:
Spoiler:
Sound Direction & Lead Music Composition: Takeru Kanazaki
Music Composition: Yasuhisa Baba, Takafumi Wada (Dimension Cruise), Shoh Murakami
Performing Music:
Violin: Koichiro Muroya, Masahide Denda, Aya Ito
Viola: Reiichi Tateizumi, Takahiro Enokid
Cello: Masateru Nishikata, Shin-ichi Eguchi
Trumpet: Kenichi Tsujimoto
Trombone: Shinsuke Toriduka
Horn: Otohiko Fujita
Flute & Ethnic Whistles: Hideyo Takakuwa
Oboe: Satoshi Shoji
Clarinet: Kimio Yamane
Fagotto: Masashi Maeda
Chorus: Tamami Shiraishi, Minako Kasahara, Terumi Boku, Hiroko Kagata, Mikihiko Kawase, Dai Nishitani, Nobuhiro Minagawa, Takashi Kiyomi, Shin Sugie, Taki Shima
Vocals: Marie Kocho, Janis Crunch
Guitar: Harutoshi Ito
Instrumental Recording & Editing:
Recording & Mixing Engineer: Takafumi Wada (Dimension Cruise)
Musician Coordinator: Yoji Sugiyama (Witchcraft)
Recording Operator: Ryosuke Kawasaki (Dimension Cruise)
Mastering Engineer: Takanari Oyama (Studio O3 Tokyo)
Recording Studio: Dimension Cruise Studio
Fire Emblem Echoes: Shadows of Valentia
Ending Theme "Heritors of Arcadia"
Vocals: Bonnie Gordon
Lyrics: Toshiyuki Kusakihara
Music: Takeru Kanazaki
Sound Supervisor: Yuka Tsujiyoko