1)
What is the meaning of "va'Yir'u [Banav Es ha'Derech]"?
1.
Radak citing Targum Yonasan: They showed him. This is like va'Yar'u (Hifil).
2.
Radak: They [previously] saw [the way, and told their father].
2)
Why does it say "Asher Ba mi'Yehudah"?
1.
Malbim: Since they knew the way he came, they knew the way he returned. There were only two paths; [since Hashem forbade him to return on the same path,] they knew that he went on the other path.
