Binyamin's descendants were taught above (7:6 and onwards)!
'Rashi', Radak (7:6): Some of his descendants were taught above 1 . Here more is taught, to trace Sha'ul's lineage back to him.
Redak citing Meforshim, Malbim: No. This Binyamin and everyone listed until Naftoli (13) are from Bnei Yisachar.
Ashbel was Binyamin's third son, not his second!
Redak: Since Becher is not listed here, Ashbel is second among those listed here.
Why is Becher not listed here?
Rashi (Bamidbar 26:13, from Yerushalmi Yuma 1:2): After Aharon died, the cloud departed and Kena'anim attacked. Yisrael began returning to Egypt. Bnei Levi chased and fought them; several families were wiped out in the war. (Rashi discussed why families are omitted in Parshas Pinchas; this answers also our question. - PF)
Redak: He was listed in Vayigash among Binyamin's 10 sons, but not in Pinchas - there, only five sons are listed. Perhaps only Roshei Mishpechos are listed there and here. In Pinchas, Ard and Na'aman are called Bnei Bela; in Vayigash, they are called Bnei Binyamin! Perhaps there included grandsons together with the sons. Or, Bela named two of his sons like Binyamin's sons.
Radak citing Bamidbar Rabah 21:8: Families of Shimon and Binyamin were wiped out due to [Zenus 1 via] Bil'am's counsel 2 .
Malbim: Becher, Gera and Rosh did not father families.
Midrash Tanchuma says that the families died in the plague that came. Rashi asserted that the plague killed only Bnei Shimon! The Yerushalmi (Sanhedrin 10:2) says that more than 150,000 Yisraelim were executed for idolatry via the Zenus. (PF)
Radak: How can the Midrash explain why Becher is omitted in Pinchas, but is included here and was counted in the days of David?
