1)
Why does it say, "we are destroying"? Only one angel was sent to destroy!
1.
Hadar Zekenim #1: Both of them were sent to see the deeds of Sedom, to be witnesses that it is proper that the city be destroyed.
2.
Hadar Zekenim #2: Sedom could not be destroyed until Lot was saved, so even the angel who was sent to save Lot was needed for its destruction. 1
1
Gur Aryeh to 18:2 says likewise; refer to 18:2:1.2:1.
