According to Renfe, the renovations affecting the railway in Andalucía are scheduled to be completed on September 5, however, I doubt this will happen.
Back in 2015, while planning a trip to Andalucía with my elderly mother, there was railway construction/ renovation going on, and Renfe did supply alternative transportation.
However, I opted to travel by ALSA BUS, instead of having to deal with transferring from train to bus during the journey.
ALSA buses are air conditioned and comfortable. Your friends will have to place their luggage in the hold below before boarding the bus.
The bus station is on the outskirts of Granada so they can take a city bus, or a taxi, into the historic center. We took a taxi and it was fairly inexpensive.
Make sure your friends have booked their Alhambra tickets already.
Wishing them a wonderful trip!