At one point in the game Lae'zel runs off to speak with another character. If you run after her too quickly it will exclude the other members of your party, since they have to climb down after you. If a certain member isn't in the dialog, the scene almost doesn't even make sense.
I think if your party members are within line of sight (up to so many feet), grouped together, and not in stealth they should automatically be in the dialog.
