Who has to pay the demolition costs for container construction?

As sad as everything is: what now about the residential container?
1. I don’t believe in costs of €45,000 for a "demolition". You can probably sell it well to self-collectors.
2. Either the residential container belongs to the person who ordered, bought, and paid for it if it is a movable object. If it is a real estate property, then to the person who owns or leases the land.

Since your question should first clarify who inherits what when and why or why not, in order to answer the question, an extensive inquiry with background would have been useful. Because who has to bear the demolition costs explicitly depends on who inherits what and who owns what.

If there is a will in favor of your aunt, she inherits everything and has to pay you and your brother your compulsory portions (share of the inheritance after deduction of all costs) in cash. If debts remain, you have to participate in them or renounce the inheritance. That is part 1.

If the property belonged to your father, everything including the container and its disposal is part of the inheritance and thus your compulsory portion. If the property belonged to a third party, it must first be checked whether it is a real estate or not. If it is, it also belongs to the property owner, and he must take care of it, unless there is, for example, a rental/lease agreement that provides for different regulations. If it is not, then the container belongs to the inheritance and the disposal is the responsibility of the heirs. This is a general answer, because there may still be contracts between the father and the property owner that the heirs may have to fulfill. Then it might look completely different.

I just uploaded another picture. Unfortunately not completely visible… in the last post also the approximate size. Ok, since I have no knowledge about this at all, I have now "accepted" the amount of €45,000.

It is a container, double-decker. Allegedly (according to the lawyer, the container components "must be dismantled and disposed of with great effort")

listed as an asset in “Aktiva”: plot size 300 sqm of which 120 sqm concrete support. 181 sqm x €2.70

Based on the picture, I also assume so. But based on the picture, I am firmly convinced that it is a building = house, because for this structure you definitely need a building permit as well as all public connections. You cannot just place such a container house on someone else’s meadow. It is exactly like a brick house. Therefore, the contract design will be interesting (with the person who owns the land).

Suggests that it is owned by the father.

A building permit was apparently not available, the building authority repeatedly admonished the container construction.