1)
Did also Avishai kill Avner?
1.
Radak: He was with Yo'av when he killed him, and consented, so it is as if also he killed him.
2)
Why does it say "Hargu l'Avner"?
1.
Rashi: This is like Es Avner. We find like this - "Ashkah Li Arveni" (Yirmeyah 38:14) is like Ashkah Osi. "Refa Na Lah" (Bamidbar 12:13) is like Refa Osah
3)
Why did he say "ba'Milchamah"?
1.
Radak: Avner killed Asah'el in war, and they killed Avner amidst Shalom. This is like David said "va'Yasem Demei Milchamah b'Shalom" (Melachim I, 2:5).
2.
Malbim: Do not say that they were Go'elei ha'Dam, and were permitted to kill Avner. Avner killed Asah'el in war - this was permitted! 1
