Floor plan of a single-family house approximately 190m² and placement on the plot

Regarding the draft: the angled position of the table indicates that a straight position with seating might be tight with the corner seating. But of course, you can do it that way.
A technician will also have to get to the hot water storage tank at some point with his water pipe wrench (or whatever he uses).
You have no storage surface, that’s been established. Except under the stairs. The attic has to be used for suitcases and decorations.
Kitchen: just draw in a normal common island, 90 nothing splashes behind it. Then the placeholder seats would already be gone, right?

Back then, the plot had to be divided into equally sized parts. So a small and a large plot was not allowed.

my father will get the other 242 sqm.

It seems to me that according to Par 34 the plot of land for the existing house is too small.
I don’t see it that way yet and also advise a building inquiry.
Orally on the phone without a plan, one tends to forget facts that the building authority then approves non-bindingly, since they assume in case of questions that the facts have been explored and are conforming.

Thanks for your reply, I don't quite understand what you mean by that.

Maybe you should consider that we do not know the situation. If I ask how large the property will be, and you say that your father's property is 200-something, then we have to believe that here. Accordingly, we build the answers here. With false or unmentioned facts, we cannot advise you on anything.