"They are leaving now."
Translation:Ellas salen ahora.
Irse means 'to leave', so his usage of se is correct. Using ahora with the durative periphrasis normally signifies a change of state, since the periphrasis itself tells you that the action is ongoing.
The ahora in the original correct sentence clarifies that they are leaving now, and not at another time.
That's what 'now' is doing in English, the English progressive tense can also be used for near future, that's not the case in Spanish.
Other correct translations are:
- Se están yendo
- Ya se están yendo
- Ya se van
"Ellos estan saliendo ahora" was marked wrong. But "are leaving" = "estan saliendo", right?