COMMENTARY on 12:80
A. Yusuf Ali:

Translation:
Now when they saw no hope of his (yielding), they held a conference in private. The leader among them said: 1752 "Know you not that your father did take an oath from you in Allah's name, and how, before this, you did fail in your duty with Joseph? Therefore will I not leave this land until my father permits me, or Allah 1753 commands me; and He is the best to command.
Commentary:

1752  Kabir may mean the eldest. But in 12:78 above, Kabir is distinguished from Shaykh, and I have translated the one as "venerable" and the other as "aged". In 20:71, Kabir obviously means "leader" or "chief, and has no reference to age. I therefore translate here by the word "leader", that brother among them who took the most active part in these transactions. His name is not given in the Qur'an. The eldest brother was Reuben. But according to the biblical story the brother who had taken the most active part in this transaction was Judah, one of the elder brothers, being the fourth son, after Reuben, Simeon, and Levi, and of the same mother as these. It was Judah who stood surety to Jacob for Benjamin (Gen. 43:9). It is therefore natural that Judah should, as here, offer to stay behind.

1753  The pledge he had given was to his father, and in Allah's name. Therefore he was bound both to his father, and to Allah. He must await his father's order and remain here as pledged, unless Allah opened out some other way. For example the Egyptian WazTr might relent: if so, he could go back with Benjamin to his father, and his pledge would be satisfied.

 

Muhammad Asad:

Translation:
And so, when they lost all hope of [moving] him, they withdrew to take counsel [among themselves]. The eldest of them said: "Do you not remember 81 that your father has bound you by a solemn pledge before God - and how, before that, you had failed with regard to Joseph? Hence, I shall not depart from this land till my father gives me leave or God passes judgment in my favour: 82 for He is the best of all judges.
Commentary:
81  Lit., "know" -but since this expression denotes here remembrance rather than knowledge in the proper sense of the word, it can be suitably translated as above.
82  I.e., "enables me to win back my brother Benjamin".