1)
Why does it mention specifically Sichon and Og?
1.
Radak: (a) They fought them first (before the kings of Eretz Kena'an). (b) They were mightier than all of them - "v'Anochi Hishmadti Es ha'Emori Mipneichem Asher k'Govah Arazim Gavho v'Chason Hu ka'Alonim" (Amos 2:9).
