Self-condemnation EX?

So Judah starts relaying what happened from their last visit, and he says something really interesting

And we said to my lord, 'We have a father, an old man, and a child of his old age, who is young; his brother is dead, and he alone is left of his mother's children, and his father loves him.'

- Genesis 44:20 NKJV (emphasis added)

For comparison, in Genesis 42, they told him,

"Your servants are twelve brothers, the sons of one man in the land of Canaan; and in fact, the youngest is with our father today, and one is no more."

- Genesis 42:13 NKJV (emphasis added)

They know that they sold him into slavery... right?

Did they convince themselves that he was dead, or maybe even that they killed him, considering how they talked amongst themselves when they were thrown into prison?

Then they said to one another, "We are truly guilty concerning our brother, for we saw the anguish of his soul when he pleaded with us, and we would not hear; therefore this distress has come upon us." And Reuben answered them, saying, "Did I not speak to you, saying, 'Do not sin against the boy'; and you would not listen? Therefore behold, his blood is now required of us."

- Genesis 42:21-22 NKJV

Judah's character arc peak

By the end of the chapter, we can see just how much Judah, if no one else, has grown since they sold Joseph into slavery. I'd like to imagine that, though they hated Joseph because he was their father's favourite and he seemed to carry himself with that fact in mind, their hearts must have been severely pricked seeing their father mourn so heavily for his child, that this was something that they did to Jacob.

Perhaps they actually did believe that they killed Joseph, or at the very least, that they caused Joseph to be killed (Hiphil stuff), so, when Benjamin's ability to go back was at stake, Judah was willing to stay there as a slave in Benjamin's place because,

"...when I come to your servant my father, and the lad is not with us, since his life is bound up in the lad's life, it will happen, when he sees that the lad is not with us, that he will die. So your servants will bring down the gray hair of your servant our father with sorrow to the grave. For your servant became surety for the lad to my father, saying, 'If I do not bring him back to you, then I shall bear the blame before my father forever.'...For how shall I go up to my father if the lad is not with me, lest perhaps I see the evil that would come upon my father?"

- Genesis 44:30-32, 34 NKJV (emphasis added)

In all actuality, Jacob might have literally died from the sheer shock of knowing that the only remnant of Rachel is gone. If not, then his trust in his sons would've been shattered.