Playback individual voices?

3 staves is the easiest way to get what you want and the only way to print.

If you want to play them back separately, they will need to be on separate staves. But sometimes it is easier to do the writing out on a single staff. If you find that to be the case, you can write all four parts on a single staff (using a separate voice for each part, of course), and then use Edit -> Tools -> Explode to have MuseScore automatically move each part to a separate staff. (You must first have created a staff for each voice below the staff you are writing the parts on before using this command.)