PARMI or ENTRE
rafaelnelvam posted this helpful comment on another page:
"Entre is used when there is question of two: between his hands, between his arms, between him and me. "Parmi is used with a collection of objects and always demands after it a plural noun or a collective noun: among men, in the world ... "Parmi always requires a plural or collective nouns. "There are cases where one can use either entre or parmi when the complement is a plural."
Source: Grammaire Nationale par Louis Nicolas Bescherelle in Google Books
Imagine yourself being a part of a huge crowd and you cannot find your pals, so then you would call them, or they would call you and ask you where you are, you would say i am among you guys but cannot see you, then you would describe them where you are and you would finally find them...i was in a situation like tihs several months ago, unfortunately i did not had a phone back then, so i had to do it the harder way ;)
Tu is the familiar form of vous. Pure and simple. Usage is given to use tu via tutoyer only "on peut se tutoyer?" And getting "Oui" as a response before ever attempting to refer to someone as "tu". Extremely rude to use the familiar unless that permission is granted. Only exception is with immediate family but not for inlaws under ANY circumstances
I also imagine there's an issue of meaning difference: 'parmi' suggests a degree of integration, whereas 'avec' is simply a connection. On the other hand, 'avec' can take on (I believe?) more non-literal connotations (e.g. moral support, etc.) than I've ever known 'parmi' to. Despite these differences, though, there is a fundamental similarity to the words' meanings. So, 'with' sort of functions as an appropriate translation of 'parmi' in that it shares the same basic meaning. However, that doesn't mean they share usage patterns / roles.