Is spending on a divorced sister and her two children, whom their father does not support, considered sadaqah or zakat?

The poor sister's maintenance is obligatory upon her able brother according to the Hanbalis and Hanafis, unlike the Malikis and Shafi'is. As for the children, their maintenance is upon their able father. If he is unable or refuses, it is permissible to give them Zakat due to their poverty. It is not permissible to count what is spent on the sister and children as Zakat unless it is given into their possession with the intention of Zakat. What is spent without being given into their possession is not considered Zakat but rather charity.