I know the solution!
Go to Harry Potter, borrow the tent that looks from the outside like a small two-person tent, but inside has the dimensions of a single-family house. That should do the trick!!!
No, honestly, you won’t succeed in squaring the circle either.
Never ever would I build new and then have to walk from the bedroom through the living area to the bathroom. I wouldn’t even rent something like that.
The tiny kitchen would only be bearable in a holiday apartment, but for a family of four with possibly visitors (or the old mother-in-law who drops by for a meal)?
You’ll have to swallow a toad. Maybe think about over 1.5 stories after all.
An accessory apartment as a flat-roof extension, main house 1.5 stories with the sleeping area upstairs and children downstairs or vice versa.
But you yourself realize that the floor plan has massive weaknesses, yet you want to keep everything as it is. That won’t work. At most, you get a correspondingly large plot and can make the footprint significantly bigger.