Andronicus and Junia were in Rome at the time Paul wrote Romans. Junia' is almost certainly a woman and, if so, most likely wife to Andronicus. But they were probably known to him independently of their common commitment to Christ. Jews kept tribal lists and knew who their fellow tribe members were. But since Andronicus and Junia, as 'apostles' who saw the Risen Lord during the 'forty days,' it most likely means that they had some association with Christ prior to his resurrection.
Questions leap to mind.
We cannot know, but we can stroke our chins as we ponder these questions. Andronicus and Junia had been imprisoned with Paul. Perhaps such an imprisonment occurred in the early fifties in Ephesus. Perhaps they do. It is likely they were living in Israel, became followers of Jesus in Israel, saw the risen Christ and became travelling apostles, preaching Christ.