Hi, I'm Howard and welcome to JA. Well, after 20 years as a teacher you must be aware that generally speaking, closed families generally mean something isn't right. However, it is possible that she is just totally melded into this family and does not have time for her siblings. I am guessing that the 2nd statement is not accurate. I would guess that you have pretty good instincts and if something doesn't look, smell, sound right, it probably is something to raise your awareness about. If you sense that she is caught in a controlling relationship, I think you may have good reason.
Thanks for the confirmation that she may be in a controlling relationship. I always assumed that some sort of overt abuse must be taking place as well for someone to be in such a relationship. That doesn't seem to be the case here. It is more of an insidious, manipulative thing. I will see what I can find out about this kind of control. For now, I am being patient and always accessible to her. I do not initiate contact with her and try to always play by the new "rules" so that I won't be completely shut out. My only plan for now is to outlast him and hope that my sister sees what is happening in her life.