Or HaChaim on Genesis 42:37/אור החיים על בראשית מ״ב:ל״ז

1 לאמור את שני בני תמית, saying: "you may kill my two sons, etc." The reason the Torah inserts the expression לאמור at this point is that Reuben was not willing to utter such a sentence outright, seeing that even a conditional curse by a wise man may have fatal consequences (Makkot 11). He phrased his offer in such a way that the meaning was unmistakable though he did not actually speak about killing his sons.

2The reason he said ואת שני is that he referred to two of his four sons.

3The word תמית is to be understood as "you may punish." We find a similar punishment being inflicetd upon Aaron, when G'd killed two of his four sons as an expression of His anger at Aaron's share in the sin of the golden calf. Compare ובאהרון התאנף Deut. 9,20. Vayikra Rabbah 7,1 makes this point. Reuben made it clear that he did not want to risk losing more than two of his sons if he failed to honour his guarantee of Benjamin's safe return. His reason was that if he risked more he would nullify the merit of having fulfilled the commandment to be fruitful. He therefore risked only something that would not impair his standing in the Hereafter. Yehudah understood Reuben very well; this is why he undertook to risk even his life in the Hereafter in order to secure Jacob's consent to take Benjamin to Egypt and to secure their lives in the present world first (compare 43,9).

4תנה אותו על ידי, "Put him in my charge, etc." Perhaps Reuben's knowledge that he had no share in the guilt of selling Joseph gave him confidence that both he and Joseph would return unharmed. He alluded to the fact that only he was able to have such confidence seeing the other brothers bore the guilt of having sold Joseph, by twice emphasising "entrust him to my hands," and "I will return him,"