The third verse (9) describes how the brothers exchanged opinions among themselves. Some suggested that Yusuf be killed. Others opted for throwing him into a desolate pit so that the thorn in their side could be removed and they could thus become the sole recipients of their father's attention. As for the sin they would be earning for themselves by killing or throwing him in a pit that was something which could be taken care of later when they could repent for what they did and thus become righteous. This is the meaning of the sentence: وَتَكُونُوا مِن بَعْدِهِ قَوْمًا صَالِحِين (and after that you may become a righteous people) according to some reports. And the verse could also be taken to mean that things will come out right for them after the killing of Yusuf because that focus of the father's attention on Yusuf (علیہ السلام) will not be there anymore, or that they would, once they have apologized to their father after the killing of Yusuf, become normal as they were.
This proves that these brothers of Sayyidna Yusuf (علیہ السلام) were not prophets because, in this case, they had committed many major sins, such as, the intention to kill someone innocent, disobedience to their father and causing pain to him, contravention of pledge, conspiracy, and things like that. Such sins, according to the Muslim consensus, cannot be committed by the noble prophets, may peace be upon them all, even before they are ordained to be one.