Thanks man you're a hero!

No, it's not possible to play with Jong clubs. Spanish and German youth clubs are integrated differently than most youth/reserves teams: they're their own separate club linked to the main club by an affiliation, which is why you can manage them. They can have their own budget, and they can even have their own board if you so desire (check the pre-game Editor). German and Spanish youth teams are more independent relative to their main team.

Also IMO and IME, managing Real's La Castilla is a pretty miserable experience in FM. The manager of the main squad just takes every good player and lets them rot on the bench of the main squad. Your hands are tied, you can only do tactics and matches, you don't get to decide on much else.

is it possible to play with teams like jong psv ? because you can for example play with jong barca and bayern so why not them

Xavier, you are such a legend. Thanks a lot for this!

they are all unavailable for me?

Hello, no there's no plan to go below what's available. The complexity of the promotion system already deterred me from adding the Derde Klasse, as explained in the thread above.

The second reason is that FM doesn't scale that well that low in the pyramid. Essentially it means that past a certain point, there's no difference between clubs that can be two or three divisions apart because FM doesn't have the resolution to scale that low. And with the Tweede Klasse, you're already near rock bottom of what FM can do and still be pleasant to play.

Is there a plan to add derde and vierde klasse?