Floor plan design for narrow lot

I think more can be made out of it. The wardrobe is just a narrow hallway. Why not extend the utility room all the way through there and put the wardrobe at the front, for example under the stairs? You can definitely get more out of that space. With 27 sqm, the living room is quite generously sized, the eat-in kitchen is too small. It may seem spacious, but the drawn counter/island is only 60 cm deep, whereas usually around 90 to 100 cm is aimed for. Separate toilets are a matter of taste, but if so, please not too narrow. You should still be able to turn around so that you can clean them after use. For the ground floor I find the bathroom situation unnecessary; if a shower is desired, the toilet can be integrated there. Then you have space for a broom closet or shoe room. The walk-in closet can be a bit wider, taking the space for it from the bedroom, since that is also generously sized. It makes more sense to access the bedroom from the dressing room so that the person who is still or already in bed is not disturbed. The separate WC on the upper floor could use more width.

With 27sqm, the living room is quite generously equipped, the eat-in kitchen is too small.

There are 27sqm for living/dining.
The living area is about 4.5x3m.

If it's enough, I don't think the priority on larger children's rooms is bad.

There are 27 sqm for living/dining. The living area is about 4.5x3m.

Oh yes... that will be tight [emoji33]

red: the plot, access via green path, house would currently be at the blue location. Existing building in yellow as garage and cellar replacement.
On the western property boundary existing building of the neighbor, tall agricultural storage halls.
2 full floors possible.
"detached construction" is a must. That means building attached on at least one side, on the other side at least with a wall/gate or similar.
The plot at the narrowest point, at the very north, is exactly 12m wide. A drive-through possibility would be nice (also because of the existing garage), therefore 9m maximum width of the house.

Are these storage halls at the neighbor ... the white spot?

Does it make sense to run an access road from the green driveway to the possible yellow garage across the whole plot? To the south, everything looks quite like a concrete surface. That all has to go too - right?

What exactly is in the northwest, so above the blue house spot?
What about the plot in the northeast?

How I would change it:
Try an L-shaped staircase.

Only a guest toilet downstairs. We have 2.4 sqm and I have to say that is completely sufficient. But we also enter from the side. If you enter from the front, I would add another sqm.
I would leave out the guest bathroom downstairs.
Then the utility room: we have just under 9 sqm. It is enough for the heat pump, the ventilation system, a large cat litter box, washing machine and dryer as well as a shoe rack. The stroller is also stored there folded together.

I don’t think the storage room in the kitchen is so bad. I like it, even if it really wastes space.

Do you insist on separate dining and living areas? I would combine them to make everything a bit more generous. Then you also get some of the fireplace view when you are sitting on the couch.

You can forget about the workroom as it is. It’s just enough for a desk.

12 sqm for a bathroom is generous. We have a bit over 10 sqm and I find that we have very nice space there.

I sketched an idea. Don’t hold me to the dimensions. I drew it freehand. But this way you have an idea how I would divide the rooms to get a large hallway (which is worth gold), a proper study, and a suitable living area.