Floor plan, building with tree, granny flat, and existing buildings

More "tomorrow" during the day, for the moment first:

I attached a photo with a view from the street,

... that gives me the impression that the "basement" is misnamed. When I look at the heights from the street like this, I would rather describe the "basement" as a "semi-basement hidden in an embankment." Show some existing plans - at least I have the initial suspicion that a new building is the wrong concept here.

Have the exact dimensions of the construction window ever been mentioned anywhere? How wide is it?

the building envelope is 15m deep, the setback from the boundary is at least 2.5m (exactly it is 0.4*(wall height + roof height/3), which is 2.58m for the current design). The plot is 16.6m wide (at first I assumed 15.8m but according to the surveyor more belongs to the hedge).

The top edge of the existing floor is 1.30m above the sidewalk, no idea if that is already a basement level. The cellar is, as said, a partial cellar in the front half, which is quite damp. The walls are all somewhat crooked and built from assorted stones (mostly sand-lime brick, some brick). Outside cladding ( , not sandstone) and no insulation. The roof structure probably does not support proper insulation or photovoltaics and there is water damage around the chimney. Windows date from the early 80s, electrical and plumbing from early 2000s, but a lot of botched work. I currently don't see how it can be meaningfully modernized or dismantled – but I am open to ideas, generally like to preserve old stuff.

...there will be no sofa in the granny flat, however.

I find that bizarre. What is dad supposed to sit on all day? Or is he already bedridden? Even if so, I would still build the granny flat in such a way that a sofa could be placed. The next person to live there is probably you. How would you like it?

Yes, I also find the thing with the sofa bizarre, but for me it actually only existed once I moved out of my parents' house. However, people prefer to sit at a table (on a hard wooden chair, please no cushion). And yes. At some point, there might be a sofa in there, it shouldn't be impossible. But if you're planning more for the present, having a sofa-TV corner is simply not priority number 1.

I correct my post #62; the house is drawn too small.