Well I would take "doing sin" and "sin he does not do" and put emphasis on the "do" part as an active, purposeful doing. As we know that nobody is without sin, I think the point of these verses is that Christians do not pursue sin. Interesting I am reading a book of meditations on the Epistles of John right now and recently read this regarding Verse 9: ". . . no one can be a half-Christian, that he should bear the name of Christ and still do the works of the devil."Verse 8: “The one who is doing sin from the devil is he, because from the beginning the devil sins. For this the Son of God has been manifested, in order to destroy the works of the devil.”
Verse 9: “Everyone who has been born from God sin he does not do, because His seed in him remains; and he is not able to sin because from God he has been born.”
This is probably a much closer translation of the Textus Receptus into English.
--Samuel Heinrich Fröhlich, 1841