Boundary construction/extension obligation

As I already mentioned in another thread, we have an obligation to build an extension on the settlement house next to us on our property. It has a footprint of about 50-60 m2. Our new house is supposed to have a footprint of 140 m2 (it is supposed to be a two-family house). Now our neighbor, to whom we have to build the extension, said that we are only allowed to build where the current houses "touch" and otherwise must keep a 3 meter distance. That seems somehow strange to me and would also be difficult for us, as the property is quite narrow... Of course, we will ask the building authority again, but does anyone here have experience with this?

what kind of building encumbrances/easements exist for this (mutual?) I can hardly imagine that the building permit imposes conditions that are not binding for the other party. If that were the case, then the building permit would be invalid (because unfulfillable). Then personally/friendly request a "correction" at the building authority

that we are only allowed to build where the current houses "touch" and otherwise have to keep the 3 meter distance. That seems kind of strange to me

Then we are already two there :)

So it is indeed the case that we have to build onto the settlement house in the front again, while on the right side, where there is no longer any development, we have to maintain the 3-meter distance.

That sounds like the planning won't be quite easy.

Yes, unfortunately. Unfortunately, it is also the case that overall it is not quite easy