Is it permissible to give zakat to one's paternal grandmother, to servants and drivers, and to one's wife's sister?

Zakat is to be given to the eight categories mentioned in the Quran: "As-Sadaqat (Zakat) are only for the Fuqara' (the poor), and Al-Masakin (the needy) and those employed to collect (the funds); and to attract the hearts of those who have been inclined (towards Islam); and to free the captives; and for those in debt; and for Allah's Cause, and for the wayfarer; a duty imposed by Allah. And Allah is All-Knower, All-Wise." It is permissible to give Zakat to the wife's sister, house servants, and drivers if they are poor or needy, and their salaries are insufficient, provided they are Muslims and the payment is not for the benefit of the work. As for the grandmother (father's mother), scholars have differed on the permissibility of giving Zakat to her if she is poor; the sounder opinion is that it is not permissible because her maintenance is obligatory upon her son or her son's son if he is wealthy.