Floor plan tips for a single-family house with a desired granny flat

The two staircases on the ground floor naturally take up a lot of space, and for this house size a straight staircase is not optimal.
A straight staircase looks great, but we will also do without it, as there are simply better solutions on an average floor area.

It is difficult to find a good solution to provide both parties with the necessary privacy while also saving space.

Would an entrance from the outside to the granny flat be conceivable? Then the straight staircase could go and where the staircase to the granny flat is now, a half-landing staircase could be placed. This would open up the entire ground floor, and the layout could be reconsidered. Of course, the upper floor and basement would also need to be addressed again.

But first you should be clear about which path you want to take. Because the building application has already been submitted. Either start over or leave it as is.

The budget has already been pointed out. That is far from sufficient. So reconsider this point as well.

The two staircases on the ground floor naturally take up a lot of space, and for this house size a straight staircase is not optimal.
A straight staircase looks great, but we will also do without it, as there are simply better solutions on an average floor area.

It is difficult to find a good solution to provide both parties with the necessary privacy while also saving space.

Would an entrance from the outside to the granny flat be conceivable? Then the straight staircase could go and where the staircase to the granny flat is now, a half-landing staircase could be placed. This would open up the entire ground floor, and the layout could be reconsidered. Of course, the upper floor and basement would also need to be addressed again.

But first you should be clear about which path you want to take. Because the building application has already been submitted. Either start over or leave it as is.

The budget has already been pointed out. That is far from sufficient. So reconsider this point as well.

Good 25 percent of the floor area for air and traffic routes,...? You can do that in a 400 sqm villa.
With your planning, you have the usable area of a terraced house, with all the usual bottlenecks.

They do that, don't they? Or am I missing something?

In the meantime, we are at the point where we might possibly eliminate the air space

Not even close. I roughly counted a full 225m2 of living space, which is about 563,000 euros, plus incidental construction costs including above-average earthworks. There's easily a 6 at the front... and nothing low behind it.

Do you have a GU contract with fixed costs? I also consider the budget extremely questionable or simply impossible. That would give me the biggest headaches.