Semi-detached house for conversion/demolition

Hello everyone,
I have an appointment at the building authority soon and will also describe these questions there, but maybe through your answers here I can already derive more concrete hints and further questions that I otherwise wouldn’t have thought of, especially under time pressure...
I have the option to buy a neighboring plot (plot B) which borders directly on my plot A. On plot B there is a semi-detached house exactly in the middle/symmetrical to plot C, on which, logically, the other semi-detached house stands. The semi-detached house has been vacant for years (in shell condition) and is, well, ready for demolition. The semi-detached house (B and C) belongs to one and the same person. The semi-detached house is structurally separated by a two-layer wall with about a 5 cm insulating strip in between at the property boundary (B & C), as well as the concrete ceiling slab. (only the base plate runs through)
As far as I have learned, no building encumbrance is registered on B & C. The semi-detached house consists of 2 full floors.

My idea: a) a conversion into an outbuilding and for that to deconstruct the upper floor and use only the ground floor. -> Is that possible, because then the gable wall from C to B would be exposed, but then again it is in shell condition anyway...

My idea b) complete demolition except for the base plate -> because of structural stability. Would that work?

What do you think?
Thanks and regards

During our search for a plot, I also came across a semi-detached house and therefore did some research. Demolishing one half is not a problem. As far as I understand, the neighbor in the other half must not be disadvantaged by it. For example, if the demolished half was insulated and is now gone, you have to provide the insulation elsewhere.

Ok thanks, the question "...the other half therefore does not suffer any disadvantage..." is of course, does this also apply to a house in shell construction/demolition condition?

Tearing down one half is not a problem.

I have to correct myself again. No problem in the sense of not being forbidden. It may not always be possible.

I think that the condition of the house to be demolished is of less importance. One exterior wall of the neighbor, which was previously built up, will be exposed after the demolition.

Yes, but should one set the insulation value/requirement there? Another idea: what if I leave my part of the gable wall standing?