What do you do about dishonest family?

[Iggy]

And Wolf, she is very defensive anyway so I agree that an intervention wouldn't do any good. But we still need to have a game plan for how we are going to treat her and what we will let her do since she is so destructive to everyone surrounding her. I would rather sis not be there for the discussion on how we want to handle the family gatherings (among other things) because she will just cry and yell and scream, and that makes if very difficult to have a civilized conversation. But the rest of the family wants her there so she knows what is going on, so she will be there.