I think the best you can do to support your wife through psychotic episodes is to familiarize yourself with her symptoms and the skills that work for her. Going through the workbook together and talking to her about what she learned in therapy and how you can help her apply the skills is a great approach (provided she is comfortable with that of course). Maybe even join her for a therapy session to get a better understanding of how and when you can support her?
If she just recently started to learn to cope with her symptoms, this might be the reason why her episodes are lasting longer this time. Sometimes confronting a problem can cause it to manifest more severely in the short term, because we are actively working on changing our perceptions and reactions to it and it thereby is inherently more present. This isn't necessarily a bad thing and doesn't mean that there will be no improvement in the long term. It's often the first step to recovery. A change in medication can add to that as well.
perhaps she is just saying she is hearing the voices in an attempt to be hospitalized.
Is there a reason for you to think that? Does she want to be hospitalized again?
He also brought up that there could be a psychological reason for the voices (low self-esteem, poor self talk, negative and dysfunctional thoughts) as opposed to a brain chemistry cause.
Those things are interconnected anyway, thoughts, emotions and behavior can cause changes in brain chemistry and the other way around. She is already getting treatment on both fronts, therapy for psychological issues and coping strategies and medication for disbalances in brain chemistry. Not sure what else your brother is suggesting?