I've not yet tried n,n-DMT and even I think doing it in a "group" context, especially with 3 doing it and 3 not... presumably one person will do it at a time while the other 5 sit there and stare.
Just sounds real creepy to me, likely to give the one dosing some very negative feelings.
Just from what I know about it, I would suggest introducing your friends to it one at a time in one-on-one sessions. With the understanding being beforehand that you will NOT interfere or attempt to influence, you are there not as a "guide" but as a "sitter" to be there to help in the very unlikely event that the person has some bad PHYSICAL reaction.
I agree it sounds so personal and inward an experience, and like tripping when I first started, doing it around others resulted in my worrying constantly "Am I acting too wierd" (i.e., the druggie version of "Do these pants make my ass look fat?" :D ). Or the people not doing it at a party who knew I was would give me these sideways glances like "So when does he start freaking out?" that no matter how discrete they thought they were being I would ALWAYS pick up on it, having such an amplified sensitivity, which would then just creep me out. Or I could not help from imagining they were thinking that, which was often worse.
Doing such a transformative inwardly warping drug that totally unplugs you from ALL group contact and identification and puts you into your very own little Big Bang spacetime bubble of a universe while in a group is a little like masturbating in a department store display window. Its just hard to feel good about it no matter how good it feels or interesting it is. We are hardwired to be VERY social creatures, and doing something so intrinsically antisocial in a group is bound to introduce "What the hell is wrong with me, doing this stuff?" sort of paranoia, even if you know beforehand they are all totally cool with it beforehand.... "In the zone" you can easily forget that, and react on much more of an imagined group-emotion gut-level, which can be not the best scenario.