Do you know if your brother is having hallucinations? Is their any history of schizophrenia in your family? The sad thing is that many family members of schizophrenics will go months or even years without realizing that their schizophrenic loved one is having hallucinations. It is generally a source of shame for the afflicted, and it's very hard for a schizophrenic to tell someone "I'm hearing voices".
I luckily don't suffer from any major mental illness, but I have studied it a lot as I'm a premed student. Furthermore I have experienced schizophrenic states in the past (drug induced with hallucinogenics), so I have a very deep understanding of psychosis.
What are the exact nature of these delusions you talk about?
Has he been diagnosed with any mental illnesses before? The answers to these questions will help me understand your brother's condition a little better.
Keep in mind that schizophrenia isn't the only mental illness which will cause delusions and possible hallucinations. Schizoid, schizotypal, delusional, and avoidant personality disorders can all cause conditions similar to schizophrenia. Bipolar disorder (in particular, the manic stages) and schizoaffective disorders can also cause delusions, as well as psychotic states and hallucinations.