My Dad was babbling total psychotic nonsense, screaming it at the top of his lungs, for a long time to me on the phone. Then I heard that he was talking to the security guard a little while later, completely normal. He needs to be in a mental hospital again. (He was in once in 2009, because the police were called when he threatened to stab a neighbor).
He needs to be put on some anti-psychotic drug, like Risperdal! But he refuses anything except valium, which he gets from a cardiologist, as he has refused a Primary Care doctor for decades. He also has congestive heart failure and is afraid that they are going to find out how much alcohol he drinks.
His own brother is a retired family doctor, and he can't talk my dad into going to see a doctor.
If they can really control the craziness this much, to focus it on their children and some strangers, then who is to say they really aren't insane, that they are just acting because they don't think they will have any consequences? They lost the ability to care, and so they are just letting it all hang out?