But either way, the way to distinguish Fi vs. Fe is not what
they're doing, but why
they're doing it. If an INTJ friend/family member is being nice and polite to you, it's probably because Fi is telling him that's the right thing to do, from a purely personal/subjective moral standpoint, uninfluenced by any external standards of morality.
It would only be Fe use if he's being nice to you because
external social/cultural standards demand it, and he sees inherent value in aligning with that, regardless of what his subjective personal feelings say about it. Fe-ers will tend to suppress their own internal feelings about something if they can see that it's in the best interest of their cultural/social group as a whole.
Fi-ers, if prompted to do something they personally
feel is wrong, will very rarely go along with it, regardless of what anyone else thinks.