The purpose of Sayyidna Yusuf (علیہ السلام) in asking these questions was to make his brothers open up and relate events fully. So, then he asked: Does your father have any child other than you? They said: We were twelve brothers out of whom one of the younger brothers disappeared in the forest. Our father loved him most. After him, he became attached to his younger real brother and that is why he did not send him along with us on this trip so that he can be a source of his comfort.
After having heard what they said, Sayyidna Yusuf (علیہ السلام) gave orders that they be lodged as royal guests and given grains according to set rules.
Sayyidna Yusuf (علیہ السلام) had established a standing rule of procedure while distributing grains. He would not give more than one camel-load of grains to one person at one time. But, once this was consumed as calculated, he would allow it to be given a second time.
Having found out all those details from his brothers, it was only natural that he would think about a second visit by them. For this purpose in sight, one obvious arrangement he made was to tell his brothers:
ائْتُونِي بِأَخٍ لَّكُم مِّنْ أَبِيكُمْ ۚ أَلَا تَرَوْنَ أَنِّي أُوفِي الْكَيْلَ وَأَنَا خَيْرُ الْمُنزِلِينَ
Bring to me your step brother from your father's side. Do you not see that I give full measure and I am the best of hosts? - 59