Strange enough, everyone suggested the straight staircase... I'll try to draw something myself.
As I said, a straight staircase always wastes a lot of space in the hallways, so I would also plan classically.
Regarding the kitchen: the idea was to make the kitchen as small as possible and really only use it for cooking.
I don't see the problem only in the size, but also in the layout. It's very cramped, or if two people work together, they are constantly in each other's way. Also, I see too little workspace. You still need at least a tall fridge and probably another tall cabinet (oven, pantry, etc.). That leaves not much room for working, even without microwave, Thermomix, Kitchen Aid, etc. Additionally, I find the paths too long. Overall, I don't like the living room yet, either. The wall unit, the dining area, and the sofa corner seem to be placed like three isolated units. I like the TV oriented toward the seating area. Of course, you can also watch TV from the dining area that way, but unfortunately only half of the people present. I also find a sofa in front of a floor-to-ceiling window suboptimal.
Unfortunately, I also see little room for maneuver upstairs. It has already been said that the bedroom is borderline. With another staircase, you might gain 2-3 m², but that’s about it. Bathroom size is okay, it should not be any smaller. The kids' rooms are at least fairly well laid out. Sure, more would be nicer, but if it’s not possible, then that’s just how it is. However, I would consider whether they really should be floor-to-ceiling windows. The question here is: more space for furniture or rather something more "airy." Both have advantages with these room sizes.