Praise be to Allah, The Lord of the Worlds.
Providing for one`s brother is a good deed and a noble act that only comes from a generous person who seeks reward From Almighty Allah.
However, according to our school of thought, Shafie, this act isn't an obligation, because one is only obliged to provide for ascendants, descendants and wife.
Al-Shafie says: "A Muslim isn`t required to provide for other than his ascendants, descendants, and wife. In other words, he doesn`t have to provide for his brother, paternal uncle, maternal or paternal aunt." {Al-Umm, vol.5/pp.97}.
After clarifying that providing for one`s ascendants and descendants is obligatory, Al-Kahteeb Ash-Shrbini (May Allah have mercy on his soul) said: " It's an obligation upon every Muslim to support ascendants, descendants and wife. As for other relatives (brother, sister, uncle and aunt), they are excluded from this obligation.
However, Abu Hanifa holds the view that one is obliged to provide for his Mahrams if they are Muslims except the wife. The evidence on this opinion is that Allah The Almighty Says: "And on the (father’s) heir is incumbent the like of that (which was incumbent on the father)." {Al-Baqara, 233}. Commenting on this verse, Al-Shafie said: " What is intended, here, is the like of that in terms of warding off harm." {Moghni Al-Mohtajj, vol.5/pp.184}.
Nevertheless, if a Sharia court ruled that he is obliged to provide for his brother then providing for him becomes obligatory. Based on this, he isn`t allowed to pay the Zakah of his money to his brother because providing for the latter has become an obligation by court order. And Allah The Almighty Knows Best.