Here "sister" means she was a believer, and not a relative. Alternate translation: "Apphia our fellow believer" or "Apphia our spiritual sister" (See: [[rc://en/ta/man/translate/translate-names]])
Paul speaks here of Archippus as if they were both soldiers in an army. He means that Archippus works hard, as Paul himself works hard, to spread the gospel. Alternate translation: "Archippus our fellow spiritual warrior" or "Archippus, who also fights the spiritual battle with us" (See: [[rc://en/ta/man/translate/figs-metaphor]])