Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
It is unlawful for you to give the Zakah on your property to anyone whose expenditure is obligatory upon you.
So, it is unlawful for you to give your Zakah to your father, mother or grandmother. As for your sister, it is lawful for you to give her from your Zakah if she is married and her husband is poor or needy. However, if you are the one responsible for spending on your sister then it is unlawful for you to give her Zakah.
Allah knows best.