It's not quite clear to me what you are getting at here. You don't like the neighbor's construction? Generally speaking or because it violates regulations?
According to the OP's statement, there are several violations of the development plan, i.e. the building regulations. That means the construction is not carried out as approved, consequently there is no valid building permit, hence the construction stop. Possibly the deviations can be remedied by amendments to the building application (building encumbrances, neighbor consent, etc.), however it is questionable how extensive the required cooperation of the affected neighbors must be.
It is conceivable that the calculation of the setback areas is incorrect, but the recalculation still lies on the builder's property.
If the recalculation of the setback areas requires entries of building encumbrances on neighboring properties because there is no other possibility, that looks different.
As far as I know, the building authority is not obliged to provide information to you as a neighbor.
As a neighbor, you have full access to the building file based on your
legitimate interest, insofar as your own concerns are affected, and the building authority is therefore also obligated to provide information, as long as no rights of higher importance oppose this.
If the neighbors' consent to the construction has not yet been obtained, you still have the possibility to file an objection. However, the objection must be justified; so just because you don't like it is not sufficient. But there seem to have been massive violations of regulations here, e.g. setback areas, and this very much affects you as neighbors. So submit a written objection (justified!).
For what purpose? There is already a construction stop; more than a stop is not possible. If construction continues nevertheless, the building authority (!) should disclose under what conditions this is happening. If the building authority does not comply, deadlines should be set for the building authority. I would take note of the builder's statements, but no more than that.
To what extent the builder can possibly be forced to dismantle will be decided by the building authority. [...]
More likely a judge, but whatever. Dismantling is only an option if all other lesser measures are not suitable to bring the building project into compliance with applicable law and the impairment to the neighbors cannot be compensated by monetary payments.
If the builder/building authority continue to be stubborn, and it is obvious that the building project is only approvable with the consent/cooperation of the neighbors, I would suggest throwing a compensation sum into the mix. Maybe that will get attention.
Best regards Dirk Grafe