Thank you very much for the many responses!
Yes, we submitted the preliminary building inquiry in writing. Three binders, one for the municipality, one for the district office, one for the builder. So already a proper "forerunner" for the actual building application. Since we were initially told that no problems were to be expected, we wanted the authorities to receive as much information as possible in order to clarify any questions before the detailed planning.
So if I understood correctly, I must also receive a justified, written rejection, right? Within what time frame must this happen? I fear that this does not happen automatically and that I have to follow up (the meeting was four days ago, so on Monday).
The issue of deadlines is an interesting and very compelling reason for me to look for expert assistance as soon as possible (our architect himself says he has no legal knowledge; that is not his job after all).
Still, back to the question in the original post: after the justified written rejection (and our subsequent written objection), should I continue negotiating with the municipality or go directly to the higher building authority of the district office (only the district office can issue a building permit)?
And does anyone know a law firm in and around (west of) Munich that specializes in building law? I would also be grateful for tips here.
And one last remark about the neighbor:
He is simply angry because he did not expect that another house could be built there. I can basically understand that. Because the strip that my brother bought was initially offered to him, but with the note that he could enlarge his property with it but was not allowed to build on it. Since they could not buy under the local resident model at that time and already had enough financial obligations with purchase and construction, they declined.
My brother was then offered the land a little later as "building land." This is also noted in the purchase contract; it really says "building plot" on it. The then mayor told him (unfortunately only verbally, we were not on the ball to get that in writing): if you ever want to build a second house there, then we'll do that!
So I can understand that the neighbor is angry that the house is now going to be built there after all. But I cannot be held responsible for the varying statements of the municipality (another neighbor who also bought this strip was told something completely different; so the municipality spoke as they needed to at the time...).
On the other hand: he never uses the affected side of his garden; even the compost pile that was laid there years ago is rotting and falling apart. We fully comply with the required distances. And he will not be shaded by the new house either. We are talking about a southwest side here and before his property would be hit by the shadow our house would cast, there is already shade from existing trees there. In winter, no shadow would fall on the property from the house at all, in summer about half an hour before sunset. On the contrary, since we would probably prune or possibly also cut down one of the existing trees during construction, he would get significantly more sun.
And: nothing stays as it is. I know several cases where people were overjoyed to get an edge plot with an unobstructable view because no further building area would ever be designated there, and they now have a house in the fifth row because building did happen after all.
Such is life....