I wasn't going to mention it myself, as I don't have a particularly well tuned ear, but I hear it like Jed. They always sing as a trio, as did the Andrews Sisters, and I find their voices indistinguishable.

Perhaps in time I could sort them out. I have friends whose voices I could never pick out of the mix. Now, years later, I hear them and can catch all three voices and wonder even at the fact that in the beginning they all sounded alike to me!

But back to the QSB, their site does not indicate which may be taking which part. This might be by design. Perhaps it is part of the magic that we the listeners just hear that wonderful blend.

Try writing to them, WYSIWYG, I bet you'll get an answer!