Just wanted to give you a heads up since I've played with Dervish before so I know how his Rps play, but it seems like you may be thinking of the character classes too much in game terms. They're more to give us an idea of what you're typical play style will be (and preferred gear/powers obviously) but does not really indicate a defined role while in combat. Dervish's Rps place an emphasis on "realistic" combat, so what might be considered "tank" characters in a video game won't actually be able to do much more, or take much more damage than any of the other characters.
For example, even though my character uses heavy armor, it doesn't mean he'll be able to charge into battle and survive taking fire from five guys while he runs for cover. He may take one or two more hits than somebody wearing light armor, but that's about it.
Conversely, Crya, your character's pistol will be just as effective as taking out bad guys as my characters assault rifle. So feel free to use it liberally, enemies won't take much more than a few hits, even with shields.
Obviously you guys can have your characters stick together if you would like them to, but it's not necessary.