Without further information it is impossible to answer your question.
Where are you trying to make the reservation? For which route, date and time?
We are trying to make the reservation on the interrail website. The route that are not available are these one :
Berlin –> Prague - 11 July
Prague –> Vienne - 14 July
Vienne –> Budapest - 17 July
Budapest –> Ljubljana - 21 July
tysm
We are trying to make the reservation on the interrail website. The route that are not available are these one :
Berlin –> Prague - 11 July
Prague –> Vienne - 14 July
Vienne –> Budapest - 17 July
Budapest –> Ljubljana - 21 July
tysm
There's still a lot of information missing to give a reliable answer. As you may see: Regatdimg availability, it does make a difference if you do need 2 reservations or 10. It does make a difference if you do need a 1st class reservation or one for 2nd class. It does make a difference which train and (especially with your last trip) which route you'd like to take.
But in general availability is good for all dates. You may get your reservations here (but they are just mandatory for the first and the last trip but anyway a good idea):
https://shop.oebbtickets.at/en/ticket
It's 3 € per person. Select seat reservations only and the correct class of travel your pass is for. If you are a very large group you may split your booking.
Praha to Wien there are different operators. If you do like to take a Regiojet train (it's shown in tje timetable) you do need to do a reservation with them directly.
For the last segment (to Ljubjlana) not all possible routes are available here. The direct MAV trains need to be reserved with MAV directly (or at any train station).
Try ÖBB for your reservations. If there's a problem, ask again. But in general there's very good availability for all segments and it should work.
Budapest - Ljubljana (09:00 departure) should be available online through ČD: 77 CZK (3€).
Check back less than 60 days before departure.
