I'm not able to listen to the score right now, but this is what I can remember. Hope it helps somewhat even if not exactly able to give complete track-by-track credits:
- Kenta Nagata was responsible for defining the nautical sound of the game. Pieces such as The Great Sea, Dragon Roost Island, Outset Island, and the title theme. He also did the main character themes, such as for Aryll.
- Hajime Wakai had a major role too. As the interview Prime Blue linked to, he handled the battle themes. His cutesy Pikmin-esque fingerprints are all over quite a few themes too such as those for Forest Haven. I believe he shared dungeon music duties too.
- Koji Kondo's role was very small. The only piece I know he did is Grandma based on the Nintendo Sound Selection credits. However, I think he may have done a couple more melodies and maybe even "Farewell, Hyrule King".
- Toru Minegishi's role is mysterious, but his major interview
here emphasises how he learned to synchronize music with character animation. I'd therefore guess he did most of the event themes, which is consistent with his orchestral style.
I'm still not sure about a few things. For example, who was responsible for arranging the Zelda reprises (Nagata probably but I hear some Minegishi too) and what about those really eccentric minimalist themes (I'd guess Wakai but possibly Minegishi again). Does anyone have any further ideas?