What is the ruling on agreeing to a second marriage with the consent of all parties, and the second wife's willingness to cover expenses after the husband faces financial hardship, and does this fall under her Zakat, and is it permissible for her to pay Zakat from her own money to the husband's family?

The parties whose prior approval must be obtained for a second marriage are the husband, the second wife, and her guardian. As for the first wife, she does not need to be consulted, and the validity of the marriage does not depend on her approval.

It is permissible for the second wife to cover all marriage expenses, such as sustenance, housing, and so forth, because that is a right for her, and she may waive it, except for the dowry. She cannot waive the dowry entirely, but she can reduce it. The Prophet, peace and blessings be upon him, encouraged the reduction of the dowry and blessed those who reduced it.

As for this woman spending her zakat (definition) on what her husband owed her in terms of sustenance and housing, it is not permissible. However, paying her zakat to the husband or to his children from another wife is permissible if they are poor and eligible for zakat.