What did Yosef say that comforted them?
Rashi #1: He pointed out that he could not possibly do them harm, since, before they came to Egypt, people were grumbling that he was a slave, and it was only after they arrived that they realized that he was a free man. If he would kill them, they would say that he found a group of young men, boasted of his relationship with them and then killed them - for who has ever heard of anybody killing his brothers?
Rashi #2: If ten lamps cannot extinguish one lamp, how can one lamp extinguish ten?! 1
Ha'amek Davar: Do not feel bad that you are dependent on another's table - [normally,] the world is dark for such a person.
Why did Yosef say that they should not fear?
Malbim: I am forced to do the will of Hashem. He did all this in order that I feed you and your children.
Ha'amek Davar: Do not fear that even should I not harm you, that I will not feed you and your children. If so, it would be better that they be his slaves, and then they need not worry about income, for a master normally feeds his slaves, like I wrote (47:20)! Rather, do not fear; "I will feed you and your children."
Why did he mention their children separately?
Ha'amek Davar: This hints to his concern to feed the children what is nicest and best - clean bread and fine flour, like I explained to the verse, "Lechem l'Fi ha'Taf" (47:12).
What is the meaning of "va'Yedaber Al Libam"?
Ha'amek Davar: They are matters that the heart accepts.
QUESTIONS ON RASHI
Rashi writes: "[If] ten lamps could not extinguish one lamp..." (Megilah 16b). Why are the sons of Yaakov comparable to lamps?
Gur Aryeh: The twelve tribes represent the twelve constellations of stars, which bring light to the world. Thus, it is impossible that even one of the tribes would be destroyed. 1 That is why Yosef was saved; all the more so that ten tribes cannot be harmed.
Maharal (Derech Chayim p. 58, to Avos 1:18): Just as the constellations are all connected and are at peace with each other, so too, the twelve tribes cannot exist without each other.
Rashi writes: "[If] ten lamps could not extinguish one lamp, [how can one lamp extinguish ten]? (Megilah 16b)." But this parable omits one important factor -- Yosef was a king, and could gather his forces to overpower them!
Gur Aryeh: The parable does not say that one person cannot extinguish ten lamps, but rather that 'one lamp' 1 cannot. The tribes are invincible, not due to their physical might, but due to the significance of their role in illuminating the world (see 50:21:1.1:1).
Maharsha to Megilah 16a: One cannot use a candle to extinguish a candle! On the contrary, a candle only causes it to burn more brightly! That is indeed what happened to Yosef.