Floor plan with basement - what do you think about it?

Do not confuse floor height and room height. I think 2.6m is more likely the room height and the floor height will be around 3.0m. Have your planner show you a cross-section of the staircase.

Regarding the children's rooms. A window at the end of the long corridor will not bring in much light.

I just don't see a completed questionnaire, but multiple incomplete ones, or am I the only one?

And: Screenshots absolutely are NOT enough to assess anything, let alone recognize it. Please update everything or just delete the post here altogether.

In the second children's room it is not dark because the sun still comes in from the west, we saw it like this at the neighbors

In summer maybe in the late evening (NW) yes. In winter/spring, however, the sun sets more in the SW and not exactly in the west.

Am I the only one who only sees an unfilled questionnaire, but multiple times unfilled, or is it just me?

And: Screenshots definitely are NOT enough to assess anything, let alone to recognize it. Please update everything properly or delete the post here entirely.

Yes, many details are missing, but what makes it even more confusing is that it was copied in twice...

I would place the kitchen entrance in a slanted wall towards the living/dining area. This way you don’t run into a staircase but into the living/dining area. You do lose a bit of space in the kitchen, but it makes it cozier and more practical. However, I would start planning completely from scratch... The upper floor is just not acceptable!

You have a long way from the bedroom to the bathroom on the upper floor and also a relatively large hallway. The rooms could be made more clever and larger if you make the hallway smaller and also use the space behind the staircase.