Is it permissible to give zakat to the sister's daughter who inherited from her mother, but wants to save her money to contribute to building an apartment, and to the children of the other sister who are over twenty and work in unstable jobs, knowing that their mother is a teacher and only receives half her salary every six months?

The price of a house is subject to zakat if it reaches the [nisab] (minimum threshold) and a year has passed, before purchasing the land. As for land bought for building on it, there is no zakat on it if there is no intention of trade. It is permissible to give zakat to eligible relatives, such as the poor sons or daughters of one's sister or sisters.