Why did the brothers, or Yaakov, not send a substitute for Benyamin when Pharaoh demanded that the family produce him? Surely there were young men about his age who were quite familiar with the family whom the family would expect to do a credible job impersonating Benyamin. Do the sources discuss this?
Chizkuni 44:2 says that actually Yosef was unconvinced it was Binyamin and felt that perhaps it was a stranger from the street. Therefore he hid the goblet by Binyamin to see if the brothers will come to his aid. That way he will know it is truly Binyamin.
מה ששם עלילה על בנימין, לפי שלא היה מכירו, וחשב אולי הביאו אסופי מן השוק, ואם יעליל עליו ואינו אחיהם יניחוהו
Perhaps the brothers realized that they can not play games as Shimon was imprisoned.
First of all, the brothers knew that they could not hide the "relationship" with a ringer. They had already shown this with Yosef, when they had been unable to act pleasantly after the dreams. Consider the way they had revealed the existence of Binyamin and the way Yosef had gotten them to speak of their family.
Secondly, they realized that they were dealing with Tzafnas Paneach, he who reveals the secrets. They would have been told about the dreams and about how Yosef had been raised to his position. By this time in his career, no-one would have dared attempt to deceive Yosef in any matter. After all, people would have been trying (and failing) to trick him for (at least) the previous nine years. They would know that any attempt to trick him could cause the death of all of them.
Par'o had publicized the dreams and his displeasure with the "answers" that they had given him. He then declared before the entire court that Yoseph had successfully interpreted the dream and that had given the advice that would avoid the trouble that was coming and that he was the "wise man" who would lead Egypt. He then paraded him before the entire kingdom. The butler had announced exactly what Yosef had done.
Similarly, only by publicly announcing the famine to come and how Yosef had discovered what was to be could they justify the storage of the grain during the years of plenty. The pasuk says Miketz 41:54
And the seven years of famine began, as Joseph had said, and there was famine in all the lands, but throughout the land of Egypt there was bread.
While the years of plenty were not attributed to Yosef, the years of famine were acknowledged as the result of his prediction.
Third, Yosef had already shown intimate knowledge of the brothers. The medrash explains that he had seated them in order of their ages(which was not obvious) and had returned the money into the sack of each brother that a particular bag of money had come from. Note that it does not say that he returned the amount of money to each brother, but each brother received his money. Of course a medrash may not be fully accurate and it is not pshat, but it does show what was going on and how Yosef was regarded. Thus, it can be used to show that Yosef did have details at his fingertips that would have prevented trickery.
All of this serves to explain why they did not dare to try to fool Yosef with someone else, even if they could have brought themselves to risk an innocent party. Indeed, since they realized the wrong they had done to Yosef, they could not do a similar action to someone who had not harmed them.