Is it obligatory to give the daughters of a deceased sister their share of inheritance and Zakat, despite their ill-treatment of their mother, or is it permissible to give this share in charity on behalf of the sister?

Charity to needy relatives is better, as the Messenger of Allah, peace and blessings be upon him, said: "Charity to a poor person is charity, and to a relative it is two: charity and maintaining kinship." And because he said to Abu Talha: "And I think that you should make it for the relatives." Therefore, it is better to give your charity to your two needy nieces, whether it is Zakat (definition), voluntary charity, or relinquishing your share of the inheritance. Their bad treatment of their mother is impermissible, and they should be advised of the obligation to treat parents kindly and the prohibition of mistreating them. You must maintain ties with them by every possible means.