What is the ruling concerning zakat that did not reach its rightful recipients because the sister withheld it? And what should we do in this situation, and how is the zakat calculated now after an amount exceeding the obligatory amount for the current year has been disbursed?

It is obligatory to maintain kinship ties even amidst family disputes, as cutting off kinship is one of the major sins. If a man prepares the zakat for his wealth and it is stolen or damaged, he must pay it again. And if the owner of the wealth deputizes someone to disburse the zakat, and it is stolen or damaged while in the agent's possession, the owner of the wealth must disburse it again, because the agent's hand is like the principal's hand. Therefore, if the husband deputized his sister to disburse the zakat and she did not deliver it to its rightful recipients, then he is obliged to disburse it again. And he must now disburse the zakat for his wealth only for the year that has passed, and he is not required to disburse anything in place of the money designated for the coming year until its year has passed.