Floor plan design for a single-family house with a granny flat

This is not a granny flat, this is a guest room with its own bathroom. :) A granny flat must have a floor area of at least 23 sqm and allow independent household management.

And a separate entrance, if I’m not mistaken. So either its own front door or apartment door from a shared hallway. Here it simply branches off from the hallway/kitchen/living room/dining room.

To me, it looks more like there is an office/guest room planned on the ground floor, through which you access the guest bathroom. And the office on the upper floor will then become the dressing room.

Why do you need the granny flat? Such a small room is certainly hard to rent out. The entrance situation is totally poor. Besides, the tenant would then have free access to your rooms plus, due to the open concept, you would always be aware of when the tenant comes and goes.
With 4-5 overnight guests, a granny flat is also not worthwhile, and permanently accommodating grandma on 13sqm including kitchen is questionable.
If it is only because of the subsidy, I would consider whether the money could be saved elsewhere.
If you drop the granny flat and instead put an office there (with a sofa bed) and then a guest WC also with a shower, the problem with office access through the bedroom would also be solved and the children's rooms could be more spacious. I find 12sqm a bit small for the size of the house.
Overall, I find the design rather unimaginative and uninspired regarding office, children's rooms, granny flat, and utility room. There definitely has to be more potential.
Others know more about the terrace and heights.

Separation is ensured by the hallway, but for KFW funding the requirements for a self-contained residential unit must be strictly met. This has been monitored much more strictly since last year than before, when funding was still generously distributed and it was sufficient to mark a room with a separate bathroom and kitchenette on the building plan. DIN 4109 regulates the boundary areas between a granny flat and the main apartment with regard to impact, body, and airborne sound insulation. This then increases the construction costs to such an extent that it is no longer really worthwhile. (We are currently planning how we can accommodate the mother-in-law with us, it is not so easy under the updated funding conditions.) If you are planning with architects, they should know this as well.

Let's take a look at a real granny flat. The toilet window under the shared carport (as a landlord, you have to like that) and the window of the granny flat next to the terrace (you have to like that) are two reasons why the granny flat already fails in terms of location. Who wants to rent that?

Driveway: bridging one meter over nine meters, I currently can’t imagine that at all. I already mentioned it: nothing fits in 3D. Rather, the garage would probably have to shift up to the right on the plan…

But about the granny flat: for a granny flat, the unit would have to be enlarged, so the whole house extended by about one meter. That would benefit the living room on the ground floor, which I already consider too tight with RBM 3.88. Upstairs, the rooms benefit compared to small children's rooms. Of course, due to the stair position, everything shifts, which probably moves the children’s rooms to the right side of the plan, and the bedroom to the left side of the plan. Since the house now already has almost 180 sqm (which you unfortunately don’t notice because the granny flat and the bedroom swallow a lot of sqm) and even with the granny flat the budget is already tight because of the insane earthworks (the house is built against the slope), the granny flat and the whole house are basically out of the planning — meaning a rounded discard. Because the earthworks required just to have a terrace mean building even more slope into the plot, so this no longer counts as usable garden without extra costs, unless you lay it out terraced, which causes immense costs. By the way, what is meant by this? Is the north arrow wrong? Miswritten? I see something else.

Slope: from south to north 3 meters gradient (see attached surveying)

Surveying? The draft shown here was created with a common program available on the market under various brand names. You can enter contour lines there. I have the program, too… So this is not a surveyor’s plan!

Further: if the granny flat is adjusted in size, then you would have about a 2-meter-long hallway at the front door that you share. Whether four people want to put up with that remains to be seen. A utility room as an airlock then somehow falls away because you have not even arrived in your main apartment yet. But let it be so: the kitchen then has to be sufficient, because a freezer is no longer really useful as a storage space removed from the main apartment. The staircase must be mirrored, then you also gain the advantage of a freezer under the stairs. But you can’t fit more under the stairs than that… The sliding door to the terrace should be accessible when open. Currently wrongly placed, as the island is in front of it. Enough has been said about the niches… either deliberately built-in cupboards or rather not planned through by an amateur. The chimney flue goes away, then it’s not in the way either. Upstairs: the office can’t serve as a guest room like this, children’s rooms are too small in relation, the hallway is basically an inverted U if you count the access through the dressing room. The windows don’t make sense to me: why does a dressing room, apparently facing the street, or a small utility room have a floor-to-ceiling window? Do you imagine drying laundry on the carport roof?

Overall, I think there’s some mental knot here, and this is being presented through a draft.

And a separate entrance, if I’m not mistaken. So either your own front door or apartment door from a shared hallway. Here it simply branches off from the hallway/kitchen/living room/dining room.

Yep. This is currently not considered a separate apartment by the KfW. For me as a financier, the budget becomes interesting. 170sqm with an estimated €500K = €2,940/sqm (plus buffer). Including incidental construction costs? Including carport/outdoor facilities? Earthworks on the slope taken into account? Gross or net? I have a big question mark here - unless very solid own contributions are made (and the furnishings are cheap).