What does Genesis 42:32 mean?

Jacob's sons are telling him what happened when they attempted to buy grain in Egypt (Genesis 42:1–5). The lord of the land accused them of being spies (Genesis 42:6–12). They don't realize that the man they bow before is the brother the sold into slavery twenty years earlier (Genesis 37:28). When that man—Joseph—demands they leave one man behind and bring their youngest brother to prove their innocence (Genesis 42:18–19, 24), the men realize this is divine punishment for their earlier crime (Genesis 42:21–22).

Attempting to reassure Joseph, whom they only know as an Egyptian vizier, the brothers told him they were all sons of their father. They added the detail that they had two more brothers (Genesis 42:13), one they presumed dead, meaning Joseph, and another who remained with their father: Benjamin, the youngest. They would have known, now, that revealing Benjamin's existence (Genesis 43:6) opened them up to what they must tell their father next (Genesis 42:33).