Seeing as Ya'akov had only one brother and there was only one Esav, why does the Torah see fit to mention them both?
Rashi: Ya'akov 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 (Ya'akov) was in Charan.
The Beis ha'Levi: Ya'akov was afraid, not only of Esav ha'Rasha, but also of Esav [who acts like] his brother, whose influence would be bound to affect him and his family adversely.
See Kesuvos, 103a.
Why did Ya'akov 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.