Rashi (Bereshit 43:30), quoting the Talmud (Sotah 36B), tells us that Binyamin named each of his 10 sons in honor of Yosef.
Many of the names indicate that Binyamin knew that Yosef was alive, in exile, and in captivity. He even knew that Yosef was married. From that Rashi:
- [My first son was named] Bela because he (my brother) was swallowed up (נִבְלַע) among the nations.
- [My third son was named] Ashbel because God put him (my brother) into captivity (שְׁבָאו ֹאֵל).
- [My ninth son was named] Huppim because he (my brother) did not see my wedding (חוּפָּתִי), neither did I see his wedding (חוּפָּתוֹ).
- And [my tenth son was named] Ard because he (my brother) descended (יָרַד) among the nations.
Why didn't Binyamin think that Yosef was dead? The brothers had returned with a story that Yosef had been killed by a wild animal, and no one disputed the story. Binyamin wasn't present at the sale to know any differently (Rashi 45:12), so why should he think otherwise?