To add to what justkt said, there's no reason why characters who have known each other for years and years wouldn't "comment" on each other's character traits - in fact, those are precisely the kind of characters who would. Maybe not directly to one another, but at least in their thoughts and actions. Something like (from George's POV): "George picked up the check. He always paid for dinner, because Fred was a miserly bastard." (Kind of bad writing, but it's just an example.)
Just because George has this thought about Fred doesn't mean he doesn't like Fred, but it does show George's attitude toward Fred on this particular matter, and it also tells us something about Fred.
As justkt said, that's not the only way to "introduce" characters or help your reader learn more about them - but don't let the fact that your characters know each other well stop you from writing their thoughts on each other and commenting (gossiping, even) on one another. The truth is, friends and family are far more likely to do this accurately - acquaintances and strangers can only give impressions, which may not be accurate at all.
A lot of how you do this depends most upon whether you've chosen Third-Person Limited, Omniscience, First-Person, etc. If it's Third-Person Limited, then we're always going to see everyone else through the eyes of one person (even if the viewpoint changes from chapter-to-chapter) and we'll be much closer to that characters attitude and his view of the others. If it's Omniscience, then you have room to move around from person-to-person, giving us a broader sweep of thoughts and attitudes, but at the expense of not letting the reader get too close to any one character. It's up to you, and whatever best serves your story.