Sayyiduna Ali (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) ruled: "Debt comes before the bequest, while you recite: 'after any bequest which is made, or debt' [Surah al-Nisa: 12]. And the children of the (same) mother inherit from one another to the exclusion of the paternal half-siblings: a man inherits from his brother through both his father and mother, to the exclusion of his brother through his father only."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12328