My family (6 of us) will be touring Sicily in late April. For travel between Taormina and Siracusa, and then Agrigento and Palermo, will we need need to book train travel in advance? In other words, do these trains sell out and can we stay flexible about which train we take?
I bought tickets before we left for Sicily for the train between Taormina and Siracusa. I did it because I didn't want to have to deal with it when we were in Sicily. It was not full. I bought day of train tickets from Palermo to Cefalu without any issues.
Do note that you have to take a bus from Taormina to the train station. The train station is Taormina-Giardini Naxos Railroad station. You can now buy tickets that include the bus ride. They say Taormina centrale. I bought them but then it was pouring rain and decided to taxi to the train station instead.
You can also download the ap onto your phone and buy tickets that way. That is what I did to purchase the tickets to Cefalu. It was easy and I didn't have to stand in line or maneuver a machine to purchase tickets. If one person is paying for all the tickets, you can buy them all in one transaction on the ap (and online).
The Taormina to Siracusa train is a regional train, not a fast train. So prices will not go up (or down) and the trains do not sell out. I just checked trains for Monday March 25, and there are several direct trains (no changes) for €11.40. Same for the Agrigento to Palermo trains -- regional, lots of trains available on Monday for €11.40 per person. You can purchase tickets on the day of travel at the train station from one of the machines or you can download the Trenitalia app on your phone and buy the tickets before you arrive at the train station.
They are regional trains. No discounts for prepurchase and no selling out. If all seats are taken (very rare except for maybe at rush hour) you simply stand, just like in the NYC subway.