Here God had blessed them with this situation, but the brothers were afraid because they knew that there was something connected to it. They knew that they were guilty of what they did to Joseph and that God was going to get them for that, so to speak. Their father also saw it, because hearing the story, he realized that the prime minister of Egypt, Joseph, whom he did not know was Joseph at the time, would be after them claiming that they stole it.
The brothers were not quite fully honest men yet, but they were learning to be. They were beginning to learn what it was like to live by truth, not lies; by honesty rather than deceit.