Create relationships within users

https://drupal.org/project/user_relationships

This module is abig one which you can use to create relationship betwwne them

remember

you need to set permissions in oreder to make it functional

add relationship types form admin

admin/config/people/relationships/add

manage

admin/config/people/relationships

then assign permissions 

and first assign permission to view other people profiles. View user profiles under user so that users can send request to each other.