Once I was listening to Dr. Laura on the radio. A caller started her statement with, "I come from a dysfunctional family . . ." at which point Dr. Laura interrupted and said, "Shw me one that isn't! What can I help you with today?"
I don't know how a cult family can be anything but dysfunctional, as the parents have very narrow guidelines as to what their children "should" do with their lives. Being reared in a cult messes people up. That is the result of dysfunction: messed-up human beings without goals or direction.
Unfortunately, when people grow up in a family where they are not supported or counted as worthwhile, they can't "just get over it" without significant help. They are habituated into thinking in certain patterns and have to overcome it. Realizing that you are an adult and the fact that your sister is the parents' "favorite" is no longer relevant.
At some point, we have to take charge of our own lives and put the dysfunction behind us. Thank God we have professional therapists on this board and with AAWA to help with that.