1)
Why does it say "Zos Na'aseh Lahem
1.
Malbim: Since the Shevu'ah was only not to kill them, but not that we will not impose on them taxes and servitude, we can fulfill the Shevu'ah and do like the Torah commanded, and Hashem will not be angry.
2)
Yehoshua addresses them in first person plural (Na'aseh
1.
Radak: V'Hachayeh is Mekor (not a conjugation, rather, like an infinitive).
