It definitely needs help from programmers. It is them to control when and how to play the tracks. I know very little about this part.
As for the soundtracks, just make sure the tracks have
- Same tempo
- Same melody
- Same duration
My experience is:
- Create a track first, do whatever we like at this point
- Make a duplication and change the instruments, the broken chords, and increase or decrease notes by octaves.
- Mixing and mastering.
In the last GMTK jam, I made one track with 5 variations so they could fit 6 different minigames. You can find the game and soundtracks here: https://basswastaken.itch.io/gamejam-2022-entry