Even a group member can become a PVP killer at any moment so dont piss someone off...LOL
Well actually you should not kill people in your group, it will
be well known on Zek that you do, and you will
have a problem finding groups later on. But kicking someone out of group first and then kill him is seen as a little bit different, especially if a player goes afk a long time or often and expect his toon to get exp... then people will start saying he deserved it... And when a mission is completed, the group is disbanded which open up new possibilities...
Sometimes group members decide to pvp each other in mutual agreement to a certain% or death. This can be okay, depending on when and where, but this can also really piss me off. I've been in groups that done this, and then when these ppl are almost dead they expect the healer to heal them, then they go again for a second try, and suddenly mobs start popping, and your group is at low health, your healer oom and you wipe.
There goes your 50pp kei and your 50pp virtue and there goes more plats for summoning corpse and rez... ending the evening with less exp and less plat than when you actually started a couple of hours ago, and you start writing a "never-going-to-group-with-this-guy-again-list"...
But basically, always know who others are in zone, always be looking over your shoulder, but primarily the real danger is from outside your group, not from your group.