Hi Deb,
See if the following two scenarios outline situations that you could see as possibilities:
Even if the brothers did not sell Yosef, they had wronged him by taking his coat, imprisoning him and, by abandoning him for a while, leaving him vulnerable to what did happen at the hands of the Midyanim. Now that the very bad results of their treatment of Yosef were clear, the brothers could have been very motivated by their guilt to try to place most of the blame on Yehuda for failing to insist that they show proper respect for their younger brother. Maybe that isn't a really good reason for the brothers to be angry at Yehuda (the brothers should have known better themselves), but being angry with Yehuda tends (maybe) to lessen their guilt.
In holding Shimon and sending the other 9 brothers back home with silver money they would find hard to explain to their father, maybe Yosef was deliberately putting them in a situation that would remind them of the time 22 years earlier when they returned home with hard-to-explain silver money and minus one brother. (At this point Yosef still thought that the brothers had sold him for silver, that's why Yosef had silver put in their sacks of grain.)
Why would he want them to bring Binyamin back to Egypt? Notice what happens when Binyamin does get to Mitzrayim -- Yosef arranges (by framing Binyamin for theft) that Binyamin will be held back from returning home while the other 10 brothers return home with money they can't explain to their father and minus a younger half-brother. Now, as the 10 brothers return home, they should be reminded all the more of that time 22 years earlier when the same 10 brothers had to go back to their father minus a younger half-brother. (Yosef had again concealed silver in their bags as another reminder because he still thought the brothers had sold him.)
