The credits are:
Credits (FC): H. Maezawa, J. Funahashi, Y. Morimoto
Credits (NES): Y. Sasaki, J. Funahashi, Y. Morimoto
This album with music from CV3 has liner notes.
There is a small conversation between Motoaki Furukawa (the host) and "three from the development team": Yukie Morimoto, Jun Funahashi and Hidenori Maezawa.
Motoaki Furukawa just ask questions, and is identified as the leader of Konami Kukeiha Club (but not as part of the development team). He also doesn't list the game on his site, nor has talked about it AFAIK, so I'm pretty sure he didn't compose. He did arrange the first track though (
also), probably that's why he's credited elsewhere.
Jun Funahashi did boss and stage 1.
Yukie Morimoto composed too.
Hidenori Maezawa lists the game in his site, as "悪魔城伝説（VRC6搭載）（FC）". In
this interview he confirms he designed the VRC6 chip, and that he didn't work on CV3 (NES), and in the liner notes he just talks about the chip. Since his name isn't listed in CV3 I'd guess he didn't compose (lacked VRC6).
Yoshiaki Sasaki probably just did the FC > NES conversion.
Thus the safest bet is Yukie Morimoto (main) + Jun Funahashi (sub) with a "maybe" for Hidenori Maezawa.