1. That is possible but what is your travel date and departure time? Then people can check what's really the case.
2. You can't book pass reservations on the Trenitalia website. The best online place to book reservations for Italian day trains is tickets.oebb.at. No pass numbers needed and no booking fees. Do NOT use "Seat reservation only” but add the Interrail/Eurail discount and then select "One-way tickets and day tickets”.

Thanks very much, all noted.  The date for 1. Is 13 June.  

Oops, and the departure time 1218…

What departure time?

There's availability on the 12:18 departure.

Reservations are optional (the app is wrong) but very much recommended.

On this train though there's an extra supplement for pass holders, which is €10 in 2nd and €15 in 1st class. You can buy that in the same way as I explained for the second train. Reservations in 1st class are free of charge when you book this way. Reservations in 2nd class are not and and an extra €3 per person.

You can also book via cd.cz/en and there you'll get the seat reservation for free also in 2nd class. You also need to add Interrail as a discount (and remove the traveller without discount). Price is then CZK 242, which is just over €10. Currently though, you'll need a VPN to access cd.cz because they've temporarily blocked access from most countries due to a cyber attack.

Thanks again.  As it happens we have 1st class passes, so I think you’re suggesting going through oebb for reservations..

Yes indeed. You'll need to select 1st class in a second step and you'll see you'll get the free reservation added automatically.