The instrumentals for the songs in BFCI 1.0 and 2.0 are constructed of GarageBand's "Apple Loops". Several loops include

Blocking Move Beat (Ending Seasons, True Legacy)

Last Episode Bells (Gone Wrong)

Contemplative Electric Piano Chords (Stabbable, Verzephobia, Who Marks The Spot, Half of Four, Budget Cuts)

Alpha Matrix Bass (Stabbable, Exited)

Cathode Synth Layers (Ending Seasons)

Cascade Synth Bass (To The Bitter End)

There's a lot more I didn't list, aswell as some I haven't found yet, such as a loop used in both the BFCI 1.0 Menu Theme and Prevented Trust, and a trap snare loop used in both For Petal's Sake and Verzephobia. (Assuming these are actually loops)

This is more than likely the reason why Zay's songs from 1.0 and 2.0 are almost exclusively in C minor. The default key in GarageBand is C major, and I suppose they just round the loops in minor to C minor, since it's a C key.

The voices may have also been made with the sampler in GarageBand, but there's no way to know for sure.