Earlier quoted context omitted.
Courts care about precise distinctions of law (that's their purpose!). Seems clear that fingerprints aren't protected, basically the same thing as your face in terms of privacy given a good enough camera. But they would effectively be asking you the question "which finger did you use to lock this phone" to which you may plead the 5th.
It'll be contempt and possibly more if you don't unlock the device with your fingerprint. It's not hard, the "precise distinction of law," is "unlock this with your finger, whichever one does it." I don't know what complicated back and forth you're imagining, but it's never occurred in any case that I've heard of. they would effectively be asking you the question "which finger did you use to lock this phone" to which…
If you would like to claim that there's no difference between the two, then you (and your hypothetical court) should have no problem with a user supplying copies of all their fingerprints when asked to unlock their phone.
That's obviously not what's being asked for, hence other people's distinctions.