Hi.... As you mentioned your brother feels as if he is a star. This type of false belief known as delusion. Delusion is a mental illness that could be cause of neurological disorder , psychiatric disorder like schizophrenia etc.
Next Steps
First of all get it diagnosed. Diagnosis is based on mental history and physical examination. He might have to undergo a few tests like EEG, MRI etc. Based on symptoms.
Health Tips
Homoeopathy helps a lot in such cases as homoeopathic treatment is psychological based and also taken into consideration past history of patient. Psychologist also plays an important role in treating such cases via counselling.