1)
Is this Binyamin ben Yakov? His descendants are taught below (8:1-40)!
1.
'Rashi': Yes 1 . Radak - some of his descendants are taught here, and later more is taught, to trace Sha'ul's lineage back to him.
2.
Redak citing Meforshim, Malbim: No. This Binyamin and everyone listed until Naftoli (13) are from Bnei Yisachar.
2)
Binyamin ben Yakov did not have a son Yedi'a'el!
1.
'Rashi', Radak: Yedi'a'el is Ashbel 1 .
2.
Malbim: This is not Binyamin ben Yakov.


