We have now looked over all the proposals again and as a real alternative, this is possible:

Then you have a very nice spacious room instead of a tiny and a narrow room, and in return a chamber or possibly a walk-in closet. For our current needs, it is not really suitable yet, since we initially prefer to have three rooms on the 1st floor (a 3rd child should not be excluded per se at the moment and we also want to keep the guest room free because we really often have overnight guests and one reason for the big house is that grandma and grandpa don’t have to rent an expensive holiday apartment all the time). But if the narrow room annoys us too much, perhaps we have a guest room in the basement, or we urgently want a chamber on the 1st floor, this would be a great alternative. If I see it correctly, the conversion effort compared to the current plan wouldn’t be too big either, right? The doors could stay and we would only have to tear down the wall between the two children’s rooms (it is not load-bearing) and build a short wall to the chamber, right? That wouldn’t be rocket science and easy to do. Or do we already have to keep something in mind with the current planning so that it can be implemented well?