Shaykh Abdul Azeez ibn Baaz rahimahullaah was asked in his Majmoo` Fataawaa vol. 14, page 302:
Q: Is it permissible to pay zakat (obligatory charity money) to a relative, such as ones brother, or their paternal uncle, or their paternal aunt, or their maternal uncle, or their maternal aunt, and the like of them?
A: If they were poor then there is no problem in giving the zakat (obligatory charity money) to them.
Rather giving charity to them is better than giving charity to other than them, due to the saying of the Prophet sallAllaahu alaihi wa sallam:
“Giving charity to a poor person is charity, and (giving charity) to a relative is twofold: charity and upholding the ties of kinship.”
[Reported by Ahmad no. 15794, an-Nasaaee no. 2582, and Ibn Maajah no. 1844, and graded as ‘Saheeh,’ authentic by Imaam al-Albaanee rahimahullaah]
As for if those relatives were his father, or his mother, or his grandfathers, or his grandmothers, or his children, or his grandchildren, whether they were males or females – he does not pay them zakat (obligatory charity money).
Rather it is obligatory upon him to give to them from his own wealth, and that he spends upon them in accordance with his ability.