I should preface this by saying I don't think official credits exist for the individual composers that make up Witch, but by digging through their other works I think I'm pretty confident in these.
In this pack,
Tracks 1-32 are by Youichi Shimizu,
Tracks 33-35 are by Masaki Sugou,
Tracks 36-48 are by Tsuyoshi Fukutomi.
The difference in the sounds of the FM patches between these three composers is very noticeable. I know those are Fukutomi's tracks in this OST, because Shimizu and Sugou are also the only composers for Marine Buster and Words Worth. Their styles are still easily identifiable in those games, while Fukutomi is somewhat of an outlier.
The only incidental proof that differentiates Sugou from Shimizu is that Sugou used to work for MNM Software, whom Yuzo Koshiro also worked on some titles with. I have a pretty firm belief that Sugou just continued using Koshiro's instruments after leaving MNM Software. This is completely circumstantial evidence, though, so if no one believes me on Sugou, that's fine.