So I just went through everything again. What exactly did you mean by swapping the kitchen and living room? I can't imagine that right now. Otherwise, we want a separate kitchen. As planned, it can also be opened to the living/dining room via the sliding door.
For pure room planning, there are only two things for me.
On the ground floor, I would ask the architects again to come up with something to utilize the space better. The entrance airlock should be bigger so it can serve as a utility room. Maybe rotate it 90° downward and the door leads out to the front door. But then the question is where the stairs go. Where they are now fits well for the upper floor, but if you rotate them 90 degrees to the right/up where the hallway is now, the access to the guest room and bathroom no longer works. So he will probably have to mediate there.
On the upper floor, I would just remove the edges in the children's rooms. In the upper one, this is actually quite easy, and the potential utility room becomes just a storage closet. Then the upper room is easily 17 sqm and a 140 cm bed should fit in easily, if not even 180 cm. The same goes for the lower children's room. Then one closet has to go. Then the question is how long the edge there is and whether a 140 cm bed fits. Otherwise, the bathroom wall would have to move down a bit and the bathroom would be slightly smaller. Both rooms would then be >17 sqm. Maybe the parents' area is somewhat large in contrast, but the kids' rooms are not tiny.