Seeing as Yakov had only one brother and there was only one Esav, why does the Torah see fit to mention them both?
Rashi: Yakov was asking Hashem to save him from his brother who did not behave like a brother but like Esav ha'Rasha.
Targum Yonasan: He was worried in that a. Esav was his older brother (whom he was obligated to honor, 1 and b. he had the merit of having honored his father for the twenty odd years that he (Yakov) was in Charan.
The Beis ha'Levi and Oznayim la'Torah: Yakov was afraid, not only of Esav ha'Rasha, but also of Esav [who acts like] his brother, 2 whose influence would be bound to affect him and his family adversely.
Why did Yakov add the suffix 'ni' to the word "ve'Hikani"?
Ramban: What he meant was that Esav would smite both him and 'his wives and their children.