I agree with BND that they are mentally ill, actually like some who had a nervous breakdown. With pieople like that you do not argue or try to prove your point because they can't see the point. They are just carrying on as if noone else exists. So keep you sanity around them otherwise they will try and get you in the hole they are in as well. It is a long recovery and very slow progress.
Have faith and don't give up. You are the only sane person around that they can do a reality check.
