Help needed! Two-family house or house with a granny flat.

We have similar plans and have been waiting (for a long time...) for the building permit. The thing is, the ground floor will very likely be larger at your place than the space you need for bedrooms, children’s rooms, and bathrooms on the upper floor. Our solution is, on the one hand, to treat ourselves to a (anyway desired) gallery, and on the other hand, to build part of the house as a single story. On the ground floor, we basically have two slightly offset rectangular parts of the house, whereas on the upper floor we build a section over my mother’s part. Each has a separate entrance, but there will also be a direct passage. It was a pretty tricky process to come up with the floor plan, especially since, due to our special situation (building in [Außenbereich]), we have to pay close attention to living space and enclosed volume, but now we are very satisfied with the result. We are working with a good architect. "Off-the-shelf" there would have been nothing according to our (partly very specific) ideas anyway, and once you start messing with ready-made house types, it often doesn’t get any cheaper either. So my recommendation definitely is: Write down your wishes as concretely as possible and then off to the architect. Oh yes, you should be fine with the square meters. We have about 250 sqm together (plus utility room, basement replacement...) and there is even a room and bathroom included for the "fourth generation" in our family.