Some things have already been mentioned here. I find the discrepancy between the living space size for you parents and the children inappropriate. Especially when looking at your remark that the children's rooms are to be made smaller. Wanting almost 50 sqm (including bathroom and hallway) for yourselves, but a maximum of 18 sqm per child is okay? Well. I find the split bathroom for the children inappropriate. To shower or wash their hair, they always have to run across the house. Furthermore, just under 6 sqm is okay for children, but for teenagers?!
My spontaneous ideas regarding the current floor plan... For example, one could:
- Convert the HTR and bathroom on the ground floor into a utility room of about 11 sqm
- Use the utility room upstairs as a "children's bathroom"
- Do without part of the 17 sqm large dressing room/hallway
- Convert the WC upstairs into a storage room for brooms/vacuum cleaner etc.
- Reduce the living/dining area so that an adjacent bathroom for the au pair/guest WC can be connected to the "multi"-room
However, it still is far from optimal. I have the feeling that the house was built around the "parent section." But it has been neglected whether the room arrangement even makes sense. Less is usually more. Clear structures and fewer winding (partly small) rooms would certainly be a bit better. On the floor space, something feasible could definitely be created that fulfills your wishes.