Earlier quoted context omitted.
While I cannot comment on the rest, Face ID has proven to work surprisingly well for me, beating even the wildest expectations. The unlock time seems to be less than half a second, so as I look at the phone, it is already unlocked. And the detection is really good too. After I shaved my long beard and went fully clean-faced, FaceID had zero issues unlocking the phone with zero hiccups for me.
> FaceID had zero issues unlocking the phone It will let a sibling in too, or at least at a point in the past.
After googling for a bit, I think I found what you have been referencing. Turns out, FaceID learns as it goes, even from non-successful attempts. So if every time your non-identical-twin sister tries to unlock your phone using FaceID, fails, and then you immediately unlock it for her with your face or password, then the system will slowly over time learn to recognize her face as well. This makes sense to me.