Importing PDF gives wrong instrument assignment

Unlike others, I've had some luck with importing PDFs. My challenge is that I've imported Sax Quartet music and the import renders them as four "Voice Oohs" singing in two different keys! I've tried "Changing Instrument" via Staff Properties, but that by default changes the notes and the key, ie transposes as if I was changing a true voice part to be played on the Sax. If I instead override and do no transposition, the notes and key signature "look correct" but the playback pitch is the same for all instruments, that is a "C" sounds exactly the same for all four instruments - plus I get red notes because the pitch is above my bari sax's range...

I've also tried adding instruments to the score, then copying and pasting - but that screws up keys and notes in the attempt to write a voice part as a sax part, so...

I'm hoping there is an easy way to correct the "instrument assignment" and get the correct notes to play (helps check the score...). Thanks in advance!!