In Shmuel I, 9:1, it says that Avi'el was Kish's father, and Ner was Kish's brother!
Radak #1: Ner called his son Kish, like his brother's name.
Radak #2: Avi'el is Ner; he had two names. Avi'el was his name; he is called Ner, because he would light Neros (lamps) in dark alleys 1 (Yerushalmi Shevi'is 3:7, Vayikra Rabah 9:2). He called his son Ner, like himself. [The son] called his son Avner, i.e. [my] Av is Ner [like my own name].
Vilna Gaon: "Ner" applies also above - he was ben Ye'i'el, and he fathered Kish. Really, his name was Avi'el 2 .
Malbim: We find that Avi Giv'on (Ye'i'el - 9:35) was the father of Kish, Ner and Nadav. Since it says here that Ner fathered Kish, this shows that he was called also Ner. It says "Avner ben Ner Dod Sha'ul", and it says "Avner ben Ner ben Avi'el.
Malbim (Shmuel I, 9:1): This shows good Midos to help the Rabim. One of them reasons why Hashem chose Sha'ul was his lineage. Kish himself was valiant; this leads to valiance in the son. He was also apt to succeed as king due to his appearance (refer to Shmuel I, 9:2:1:1) and height (mi'Shichmo va'Ma'alah Gavoha mi'Kol ha'Am" - ibid., 9:2).
We find that different sons of Sha'ul in Shmuel I, 14:49!
Redak, Malbim: Avinadav is Yishvi there; he is called Avinadav there when he died in war. Eshba'al is Ish Boshes. Ba'al is called Boshes - "va'Yinazru la'Boshes", "Samtem Mizbechos la'Boshes Mizbechos Lekater la'Ba'al." Gid'on is called Yeruba'al and Yeruboshes.
