John Gill Commentary Genesis 42:14

"And Joseph said unto them, That is it that I spake unto you, saying, Ye are spies:" — Genesis 42:14 (ASV)

And Joseph said to them, that [is it] that I spoke to you, saying, you are spies.

This proves it, at least gives strong suspicion of it; since at first they seemed to speak of themselves, as if they were the only sons of one man and there were no more, now they speak of twelve, and mention of one being at home with his father.

But since he sent so many of them, why not all? Why should one only be left at home?