Is Zakat obligatory on a debt owed to me by my brother and sister, and is it permissible to give it for breaking a fast or to a charitable endowment building?

If the debtor is insolvent or procrastinating, making it impossible for the creditor to recover his debt, then zakat is not obligatory for the creditor until he receives it and a hawl (full lunar year) passes over it. However, if the debtor is solvent and the debt can be recovered from him, then zakat is obligatory for the creditor every time a hawl passes and the debt reaches the nisab (minimum threshold for zakat). It is not permissible to spend zakat on feeding fasting individuals, or on the construction of charitable endowments, or on building mosques and schools, or on printing the Qur'an; because these are not among the eight prescribed categories for zakat expenditure.