The most important question for me remains which document or which applicable law the city could refer to in order to reject a submitted building application on the grounds that limit values are not met, which are not cited in any official document of the city/Baupilot (except in the PDF cited by the city planner). In my opinion, such a "decisive" passage should be evident to everyone before purchasing the plot (e.g., in the justification for the development plan) without having to laboriously obtain this information from the only contact person at the city who knows these limit values.
Provided my statements apply to you (that the district decides, and the municipality only contributes a vote), the city cannot reject the application, but only recommend its rejection. The rejection itself is also a legal act, and the issuer must justify and take responsibility for it. Therefore, my suggestion is to establish a consultation with this party. The district building office director will not take the blame for adopting a rejection vote from the city justified only by "mimimi I don’t like that." The city as an authority is bound by applicable law; therefore, the passive house requirement would have to be included in the textual stipulations of the development plan (and rely on the justification of the development plan) to be legally binding. The city, as the seller of the plot, on the other hand, has full contractual freedom and may desire to conclude the land purchase only with someone who shares its "private" worldview. In an extreme case, it might want to sell the plot only to a vegan whose last name starts with "Q." The sale of the land is a purely private law matter, and the city as a legal entity at this point is a corporation like a "company" and not subject to objectivity. The recognizability of the passage is sufficient in the purchase contract, which you will finally receive with a several-week notice before the notary appointment. The notary will also read and explain this. No one is obligated here for more "preliminary transparency" or even advice; conversely, you also have the freedom to withdraw from the purchase interest without giving reasons. If the (lord) mayor cares about his image, you will still receive answers to your questions.
Why the FW connection is not possible on 5 plots I cannot say (possibly miscalculated).
Then clarify this. Contact the builder service of the local heating supplier, identify yourself as an interested party in the specific plot, and ask for a written response regarding the conditions under which it can participate in the local heating supply. And please ask the seller (probably the city land registry office) for access to the land purchase contract. Lawyers have no crystal balls and cannot advise based on assumptions or hearsay. What is important, as I have already said, is the enforceability of the condition in the purchase contract that it is to be built as a passive house (and of course, it must be defined when this condition is fulfilled). As I said, I consider a locally heated house only conditionally able to be a serious passive house (for that it really must already be a very local heating house). Presumably, this is where the problem lies for these five plots (sorry, within the scope of the open pro bono consultation hours, I cannot deal with the development plan in detail but assume banal reasons).