House and garage - How best to place them on the properties?

I deliberately brought you on board in this discussion

Thank you Yvonne. You made my day.

not only I point out moral aspects here, others here would probably also put the common good before their own advantage

To classify the use of property in the sense of the owner as morally reprehensible, that is carnival as I love it: socially critical, exaggerated, striking.
By the way, I have noticed that within the entire scope of the development plan no areas are designated for children's playgrounds.

1 parcel was too small for us for a detached single-family house, so we bought two because we wanted a little "more" space in the garden.

Outrageous! While the other seven buyers have to eke out their miserable lives on miserable planting areas that do not deserve to be called gardens, the wife of the buyer lounges fatly on 400 m² of fenced lawn area. And the neighbor children look enviously at the treehouse of the spoiled TE children.

Fortunately, tomorrow is Ash Wednesday and the fool’s cap will disappear again into the wardrobe.

but I cannot follow the argument that the use by one, maybe a second resident, endangers a child-friendly living environment and disrupts the neighborhood relationship.

I don’t either, but reinforced by the fact

By the way, I noticed that within the entire scope of the development plan no areas are designated for playgrounds.

I rather expect that the children of all eleven new building plots will choose one path or the other as a common "play street" from time to time. In my childhood, all the scooters, bicycles, and pedal cars of the gathered neighborhood gang were standing and lying in one or the other driveway now and then.

the others as subordinate elements belonging to the main house

I find the immediate proximity of house and terrace not coincidental – therefore, it is logical to see the terrace as a subsidiary facility. A windscreen has a small construction depth, typically well under one square meter of floor area per element, and the terrace itself is essentially flat. In this respect, it is therefore logical not to treat it as a building at all and at most to expect that it does not pose a drainage problem.