Reservations are available but you need to:

1. Add the Interrail/Eurail discount for each passenger.
2. Choose "One-way tickets” (NOT "Seat reservation only”).

Then you'll see availability in all trains you show.

You can also book via www.raileurope.com (desktop website only).

Many thanks for prompt reply - So I need to buy these tickets at 26euros - is that right? It also says they must be printed. ? It doesn’t ask about 1st or 2nd class? 

26€ is the price for 2 people yes (2 x 13€).

You can tick 1st class below : it costs the same but you must have a valid 1st class pass.

No need to print, the PDF is enough.

A few side notes:

1. Reservations are not possible for the regional train from Colico to Milan
2. Pass reservations via ÖBB are best done for one train at a time. If you try multiple trains in one transaction, then it often will only book one of them.

I am also planning to do the Milan to Bologna train-there are no reservation free trains on this route from what I can see? 

Yes there are direct regional trains departing every 2 hours, journey time about 3 hours, you can also take regional trains with a changing, usually in Verona, taking around 3.5 hours.