Ok, I think I hear what you are talking about. I've never tried to hear piano music this closely without the sheet music infront of me. But, I think I hear four instances where all three are playing at once, and the melody doesn't ever sound like it's more than half an octave off from either the bass or the rhythm, and those could be played with one hand if you are that skilled (jazz players do it a lot).

I might be right or completely off when I say what I said, but Noriko Matsueda and Takahito Eguchi are the composers of the entire FFX-2 soundtrack, including the piano collection. They're the artists, but I don't think they are the performers. Look at this page and scroll to the bottom. I think this guy has copied the credits from the album, and it says this song is only performed by one person. I don't know.

Whatever the case, it's a nice song.