It was hard on our family to only see my father late at night when he was tired, or on weekends if he wasn't on a business trip.

was 是 be 动词的过去式，表示"是"或"存在"的状态。 hard 是形容词，意思是"困难的、艰难的"，描述某种情况或处境不容易应对。 on 在这里是介词，表示"对...来说"，用于说明某种情况或影响的对象。 hard on 是一个固定搭配，意思是"对...来说很困难/很艰难"，表示某种情况对特定对象造成了困难或压力。