Is the plot suitable for a narrow house for 5 people?

But you are not allowed (no joke)

Sorry, but you are confusing yourself with the options. If you have no slope or none worth mentioning, then you have to build your "house with a basement" high enough so that the basement as a living space and level meets the necessary requirements (windows, ceiling height). But even then a basement becomes a full floor. And a bungalow becomes a house with a barrier because of steps in front of the door.
An ancillary flat means one more parking space.

The floor area ratio refers to the living space of full floors. You can do attic extensions, but if there is no full floor, they do not count.
If you cleverly divide your 7 x 12, then you can make a parent’s floor in the 30-degree roof well. Note that the ridge direction is prescribed there. So the roof is stretched over the 12 meters. I guess you don’t necessarily need dormers since you have gables.

No, no problem. Although information from the usage template and especially the reference height are missing, I don't see any difficulties here. You can use the mentioned model as inspiration and adjust it accordingly, or you can look at the "usual suspects" (see forum search with the keyword "usual suspects" Brale / Hildmann Traumhaus / Tecklenburg / Weisenburger / Wengerter / Werner), as they build the required house type hundreds of times, often without a basement (floor plans can be found there, very similar to the Cityline 2, but with the requested eaves-attached gable roof here, usually with a roof pitch of 35 or 38 degrees). With three children, the parents sleep in the roof studio, and the storage room above the bathroom becomes their master bathroom. These models are often 12 to 12.5 meters deep and, in my opinion, fully suitable as a "template" here. I see you as exactly the target group for such models. So the "problem" looks at a rich range of solutions (even if they only differ marginally from each other). The 11ant basement rule (see external "With or without basement: a rule as a decision-making tool") considers a basement a luxury here, but of course it relaxes the house technology and storage room situation. The Goalkeeper thread may finally here not be used as a scary story about foolhardy row house construction, but as an example of an inspiration design that can also be used here (which pleases me despite strictly forbidden punctuation emoticons).

The Goalkeeperthread ) is finally allowed here not to be a horror story about idiotic terraced house construction, but instead to serve as an example of an inspirational design also usable here (which makes me happy despite strictly forbidden punctuation emoticons).

(is that forbidden?)

Ok. This is quite a thread (301 pages) – I have something to read over the holiday. ;) (is that forbidden?)

As said: I barely know anything comparable – at least off the shelf (= the usual GU suspects on the web). But: we are still in the discovery phase.

I can imagine a semi-detached house in a full semi-detached building of that size over 3 floors. However, with such a narrow single house with semi-detached house footprint, that was difficult for me. I’m also not sure whether one might even have to include the garage in the gable – see point 1.5 of the zoning plan text below.

I’m glad to hear that. I had calculated 12*7*2*.85 = 143m2 for two floors of interior space. We would still need a finished attic - or a partly finished basement for three children's rooms plus a study.