Seeing as Yaakov had only one brother and there was only one Esav, why did he see fit to mention them both?
Rashi: Yaakov was asking Hashem to save him from his brother who did not behave like a brother, rather, like Esav ha'Rasha.
Targum Yonasan: He was worried, for (a) Esav was his older brother (whom he was obligated to honor), 1 and (b) Esav had the merit of having honored his father (for the 20 years that Yaakov was in Charan).
Beis ha'Levi and Oznayim la'Torah: Yaakov 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.
Ohr ha'Chayim #1: Save me from my brother, who has merit of my father, and Esav, who has a great power and level. 3
Ohr ha'Chayim #2: Save me from my brother, if he will craftily pretend to act like my brother, and from Esav, if he will be openly evil.
Ohr ha'Chayim #3: Save me from my brother - one who wants to kill his brother should be lowered! Save me from Esav - who is infamous for his evil, even without this. A Tzadik should not fall in front of a Rasha!
See Kesuvos 103a.
Oznayim la'Torah: And from the fact that Yaakov mentioned first "mi'Yad Achi" it seems that he was more worried about the latter than about the former.
Perhaps this refers to being leader of 400 men (and each of the 400 could stand against 400 men - Bereishis Rabah 75:7)! (PF)
What does Yaakov mean by, "v'Hikani, Em Al Banim"?
Ibn Ezra, Ramban: What he meant was that Esav would smite him, and his wives and their children.
Ha'amek Davar: He was only concerned for his wives, for Hashem already promised to increase his seed greatly. He termed this "Hikani" for one's wife is like oneself. 1 "Em Al Banim," i.e. when the mother protects her children.
Ha'amek Davar: His Bris with Lavan forbade him to marry other women, even after his wives die, lest he have more sons, and others will share his inheritance.
What is "Na"?
Ohr ha'Chayim #1: It is an expression of request.
Ohr ha'Chayim #2: It means 'now' (also Pesikta Zutresa says so). I do not want that Esav will win now, and later you will return me (to supremacy)!
Why did Yaakov say that he fears "Oso"? He should say 'Mimenu'!
Ha'amek Davar: Do not say that Yaakov fears Esav's men. If so, he should say 'Yarei Anochi me'Imo'! Rather, it means 'I fear his merits' (i.e. Kibud Av v'Em and Yishuv Eretz Yisrael - Bereishis Rabah 76:2). 1
Ha'amek Davar: Similarly, Hashem told Moshe, "Al Tira Oso" (Bamidbar 21:34). Moshe feared Og's merit (he told Avraham that Lot was captured).
