I would contact IR  customer service and the train operators whether they do group deals. 

Actually making reservations and final routings will not be possible until Late summer 2023, but certainly you can start planning a preferred route now. 

I assume you have eliminated flying or, dare I say, hiring a coach.

Passes will be costing 200 to 250 euro per student plus at least one overnight.

Currently a single fare for Nov 2022 would be about 200 euro (pre purchase) with a night in Barcelona via trainline.

Grupos mas de 10: always have to use alternative ways-contact the railways direct-they all have special deprtmts for that.

Starting from MUrcia is not a nice connection-as you always have to go via Bcn-Francia.

IF you also want to do some excursion whilst in DE etc-nearly all such school/youth-groups hire a bus (coach, touringcar) as this will work out much easier. Plus the bus-comps know how to handle such things.

Thank you for your helpful advice!