Many forget that some of these sentences have inbuilt context. "We have one nose and one mouth" is either allegorical or impossible (or one heck of a conjoined twin). Since the Owl is not too big into allegory we are constrained to accept that the proper pronoun must be singular.
One of the regular online teachers here has a video which instructs folks in how to hear the difference between mi, ni, and vi. if you can find it, I recommend giving it a good listen.