1)
Why is he called Ben Paritz?
1.
Radak: He is Poretz (breaches) the fence of Emes.
2)
What is the meaning of "v'Asah Ach me'Achad me'Eleh"?
1.
Rashi citing Targum Yonasan: He did one of these to his Ach (brother).
2.
Radak: Ach is like Echad; it is also like Achas (feminine).
3.
Malbim: Even if he has a brother who did one of these good deeds of his father, [the Ben Paritz] did not learn from his father, and not from his brother.