My brother is in need. Our parents are deceased and he's not married with no children. Our relationship is very bad. Am I obliged to help him?

No. The French Civil Code does not provide for an obligation to provide support between brothers and sisters.

However, the courts do recognize the existence of a natural obligation: this means that your brother in need cannot force you to help him, but that you can help him voluntarily. However, you will not be able to claim reimbursement because you have acted voluntarily and in accordance with a duty of conscience (1100 C. civ.).