Improvement suggestions single-family house 137 sqm GF with granny flat

The submitted plans will be taken along with the purchase contract.

And then? - if you build more knee wall, will the purchase be reversed or what?

Is the granny flat and the workspace absolutely necessary? I find it way too much on too small a space. Is that what you really want? Above all, I would miss the direct access to the garden with 3 children... We currently live on the first floor and I find it very unfortunate not to have direct garden access with a child. I am really looking forward to that in our future new build. If you absolutely want the granny flat, you could possibly design it smaller, e.g. only 50 sqm and with a separate entrance. This way you could place your living area on the ground floor and the bedrooms upstairs. I would not place the stairs in the middle but rather on an exterior wall.

I wouldn't place the staircase in the middle but rather along an exterior wall.

Or just like that, but then deliberately between the areas (on the ground floor swimming pool and family, on the upper floor for example living and sleeping or similar).

I would not place the stairs in the middle, but rather against an exterior wall.

Or even just like that, but then deliberately between the areas

That won't be so easy because you want to access the roof peak. However, I would first have the size of the peak sketched out. In my opinion, the effort is completely disproportionate compared to the usable space. The whole project has been very unthought-out and amateurish so far. One can only advise not to spend a lot of money on this mess and to consult a real professional. But I am repeating myself.

That will not be so easy, since one wants to develop the roof ridge.

That works well if the staircase stays under the ridge – for example on the gable side, where the entrance currently is, which could move to the eaves side with a trapped third parking space.

The whole project has so far been very thoughtless and amateurish.

Objectively that is true, even if the formulation 11antös sounds weakly empathetic.
Subjectively, the OP has more than just squaring the circle: one hundred seventy-three wishes for one hundred thirty-seven square meters, on the one hand besides herself a Swimu along with a permanent guest brother-in-law, an allergy sufferer and three little croakers on their back who all have to fit into the nest – and on the other hand probably also panic about only having the property secured once its seller likes her building plan. From here in the gallery, we can comfortably shout "boo." Nevertheless, conjuring up suggestions from a hat would be your usual habit – but I suspect that the highly compressed wish-conditions imbalance also weighs on your creativity.

but I suspect the highly compressed wish-framework imbalance is also stifling your creativity

Yes, there are also simply - I’ll call them snap ideas - that are no longer fun to design. And that’s what it’s all about for me. When it becomes unrealistic or just too horrible, the motivation is gone.