1)
To whom does "u'Neva'arah" apply?
1.
Malbim: All of us together [will eradicate the evil].
2)
Why did Bnei Binyamin not consent?
1.
Ramban (Bereishis 19:8): There was no Chiyuv Misah for the Pilegesh. Perhaps Binyamin was upset that the Shevatim did not send to them initially, and made a verdict without them.
