Your brother is born when Rahu was in one of the 3 Gandantha points (Refer internet) and they live in a world of their own though they could be very intelligent. They are generally disassociated with worldly feelings and behave very differently. They see life in a very different spiritual angle which produces peculiar type of outlook to life. You cannot do anything about it. Usually this lasts till they reach middle age(around 50 years). Perhaps you could effect a change in him if he is put in the company of women. I have seen 3 such people in my lifetime of astrological practice.
He has a very special Brahma Yoga which is very rare.