Greetings, and thank you for your question. You have hit upon one of the quandaries of our field in your nephew's story! Efforts have been made over the years to try and standardize things so diagnoses remain consistent based upon what a person is going through. But, because we don't have imaging studies or lab tests to say for sure, we are left to decide what is going on based upon our observation, the report of the patient, and the reports of friends/loved ones. The training of the clinician can also make a difference. For example, if a person trains at a place where bipolar is stressed, they may be more likely to diagnose it over something else. The same bias is true for a clinician trained where personality disorders were stressed. With that preamble in mind, I think the best solution is thus:
(1) Get him in with a psychiatrist who is willing to do a comprehensive evaluation on him. 15 or 30 minutes is not enough time, in my personal opinion, to do that.
(2) No matter what the diagnosis ends up being, have him continue with that same person. As that psychiatrist sees him over time, his impression of what is going on will change or be reaffirmed. But this can only happen if he is seen consistently by the same person. I have found that when I saw a person and thought they had condition A, as they continued to come back to see me I actually found out they had condition B. This can only happen as you get to know a person.
(3) The doctor should be willing to have an open dialogue with your nephew. Also, it is helpful, if your nephew agrees, for you and other loved ones to be allowed to provide input into your observations on how/what he is doing.
Hope this helps get you started! Please let me know if you have other questions and if I may of further service!
One last question, her husband is not supportive of her son. He is causing more stress in her life and will not go for councelling. He just thinks he is lazy and has given her a untimatin that if he does not leave the house by July 1st, then he is leaving her. At this time she cannot kick her son out because of his illness. What should she do.