So the blue house indeed has 3 VG, I would also recognize the green and yellow as 3 VG (even if the mansard roof visually "softens" it).
The letter from the municipality, in my feeling, rather points towards lower land use to preserve a more open building style. I would therefore try to reduce the floor area ratio first. From the previous description, I gather that no basement is planned. Maybe a concept with a large apartment on the ground floor (4 rooms with garden), 2-3 smaller apartments on the upper floor (2 rooms) and another 4-room apartment in the attic, possibly as a setback floor (penthouse), or 2x 2 rooms.
3-room apartments have recently not been family apartments anymore, but apartments for high-earning couples. They might rather move to the next town. Families with a connection to the place or lower-earning singles with a workplace in town would be your customers for the 4-room and 2-room apartments. That would mean 7 parking spaces with this reasoning.
P.S.: Nice Porsche ;-)