I appreciate your concern for your nephew From the treatment it seems bipolar depression is being treated, but history seems to be of psychosis predominantly negative symptoms but nothing can be said accurately until we get to talk to him.  Kindly consult so that everything can be discussed in detail and treatment can be rationalized accordingly.

It is difficult to say much without meeting the patient but what you have described points more towards a psychotic illness with predominant negative symptoms. To rule out a mood disorder, meeting the patient becomes absolutely necessary. It is also possible that he has an ASD (Autism Spectrum Disorder) but again, we can't say for sure without meeting him. In any case, be in regular touch with your Psychiatrist. Do not worry about how long the medicines will continue. If the medicines are helping, they may be continued for long and stopped only if the Psychiatrist advises so.

Need to consult for detailed evaluation

Needs to rationalise treatment