What is the wisdom behind Jacob's — peace be upon him — agreement for Joseph to go, and then his brother, with their other brothers, despite his knowledge of the brothers' envy towards Joseph and his brother, and their previous betrayal?

The first time, Joseph's brothers took their brother after much insistence on their father Jacob, who gave them permission, and Joseph was inspired that he would inform them of their affair.

The second time, Joseph's brothers took their brother Benjamin after much insistence on their father Jacob, and they promised him to protect him. And despite Jacob reminding them of what they did to Joseph, he agreed after taking covenants from them, relying on God's protection. Jacob saw an interest and a need in that.