Is my husband's work as a post office manager Haram (forbidden) or Makruh (reprehensible), knowing that it is currently our sole source of income, and what should we do if it is Haram?

The ruling on the permissibility or impermissibility of your husband's work as a post office manager depends on knowing his duties and the office's activities. If his work is legitimate and does not directly aid in what is forbidden, then there is no harm in it. However, if the office engages in forbidden activities, such as usurious transactions, and he manages them, then this work is forbidden, and the earnings are subject to the work, making them forbidden to the extent of the forbidden work. He must leave it unless there is a necessity.