Why does the Torah write "Vehisnachaltem" and not "Vehinchaltem"?
Rashi: Because what the Pasuk is saying is "Vehisnachaltem osam li'Veneichem ... " - 'Take possession of your slaves on behalf of your children ... '.
What are the ramifications of "Le'olam bahem Ta'avodu"?
Torah Temimah (citing Gitin, 38b): It implies a. an obligation to make a slave work; b. that whoever sets a slave free transgresses an Asei.
And why foes the Torah insert the words "Ish be'Achiv"?
Rashi: This teaches us that the Isur of subjugating an Eved Ivri extends to a leader subjugating the people under his control, and a king, his subjects.