"and sons": to include the kin (as invalid for such testimony.) They are: his brothers, the brothers of his father and the brothers of his mother, the husband of his sister, the husband of his father's sister, the husband of his mother's sister, his father-in-law, and his brother-in-law.
"Every man for his own sin shall be put to death (by beth-din)": Adults die for their own sins; minors (sometimes) die (at the hands of Heaven) for the sins of their fathers.
(Devarim 24:17) "You shall not pervert the judgment of a stranger and an orphan": What is the intent of this? Is it not already written (Ibid. 16:19) "You shall not pervert judgment"? Its intent is to teach that one who perverts the judgment of a stranger transgresses two negative commandments.