Is it permissible to give zakat money to the widow of the husband's brother and her orphaned children, knowing that other relatives are sponsoring them?

If a family has an income sufficient to cover their basic needs, it is not permissible to give them Zakat, even if their father has passed away, because they are not among the categories eligible for Zakat mentioned in the verse from Surat At-Tawbah. However, it is permissible to give them charity. If, however, they do not have sufficient means, then they are eligible for Zakat, and you may disburse Zakat to them, even if you are voluntarily contributing to their expenses. This voluntary contribution cannot be considered Zakat unless it was given with the intention of Zakat.