The premise contains a geographical inversion. According to the Gospels:
They never traveled "Jerusalem to Nazareth" as a family unit. Jesus visited Jerusalem later as a child (Passover, age 12, Luke 2:41–51) and as an adult (final week).
Distance Nazareth–Bethlehem: ~130 km through Samaria (direct) or longer via Jordan Valley (avoiding Samaria). Walking: 4–7 days depending on pace, season, and Mary's condition.