Комментарий к Берешит 42:19

בבית משמרכם (literally, in the house of your ward) — the house in which you are at present imprisoned.

אם כנים אתם, "If you are really honest, etc." This verse may be understood with the help of our sages in Yerushalmi Terumot chapter 8. We read there as follows: "If a group of people travel together and they encounter Gentiles who demand that one of them be handed over to be killed, the alternative being that they would all be killed, it is forbidden to hand over anyone belonging to the group. The whole group must face death rather than make the decision whom to hand over. If, however, the person to be handed over had been named by the killers, the others may save their lives by handing over that person." When Joseph said: "if you are honest, etc.," he meant that the brothers knew full well if they were telling the truth; אחיכם אחד, your one brother will be imprisoned. There was no death threat to the brothers, hence they were allowed to choose whom to hand over for incarceration. Joseph implied that if, on the other hand, they were dishonest, i.e. spies, (which made all of them guilty of the death penalty) then, of course, they would not be allowed to hand over one of their number who had not been specified. Handing over their brother would then be tantamount to killing him. This would also be illegal as they would all have to be prepared to die. The brothers were agreeable, thus indicating that they had spoken truthfully all along. We may presume that the brothers themselves elected that Shimon be imprisoned; Joseph did not single him out.

שבר רעבון בתיכם, what will break the hunger, i.e. the harvest; this is why the harvest, תבואה is also called שבר, as we have already explained on 41,56.