They were very likely Hellenistic Jews who lived in Palestine and fled the persecution of Saul of Tarsus, eventually journeying to Rome, and joining with the Jewish colony there.
011418 Andronicus and Junia PP
7 Greet Andronicus and Junia, my countrymen and my fellow prisoners, who are of note among the apostles, who also were in Christ before me.
— Rom. 16:7