Is the floor plan suitable for a multi-generation house?

Unfortunately, we do not yet have exact measurements of the property; we are still waiting for an official confirmation from the municipality.

Unfortunately, I cannot find any more detailed information about the respective property from the official application documents. According to the developer, a distance of 2.50m must be maintained on each side.

Through all the plans we have received so far from the developer, it has basically been "tapped out" how the house could look dimensionally and also roughly in terms of price. In the exact planning phase, we then have ongoing discussions with the architect from the developer until the house is coordinated as we envision it. So, we can basically "turn the whole house around" if needed.

Do you only use the popular misnomer for the general contractor, or is he actually acting as a developer here, i.e. does the municipality allocate the plots with the condition to build with a specific construction company? Otherwise, I recommend planning with a freely chosen architect!

Bicycles ...

Maybe one could park them in the basement as suggested here

... but then access preferably from the street side or from the side outside to the basement must also be planned.

First of all:
when you reply, you don't have to tell everyone what you have already written in the previous post. Everyone participating here automatically reads the whole discussion and does not close their eyes to other people's posts.

The planned one is now more than 20sqm, twice as big

I hope it is not where the parents have their terrace. However, I fear the worst that privacy will be compromised here on this topic.

You are buying a plot of land and have no (location) plan?

The big clearing out is definitely still on the plan – the rule that everything not used for more than 12 months goes away is already stored in the back of my mind

Clearing out and tidying up is always in one's own interest if you want to have your life ordered and practical. However, it seems to me that you focus more on hoarding and stashing when you read that you store everyday items miles away in a warehouse, even though you currently live in 100 sqm. When I then read this:

In the two households, currently 4x bicycles and one child trailer are in use. The children are still too small for their own bicycles. But that should be taken into account

My father-in-law still has a workshop,

We have also already thought about a fitness room or something similar.

Want to give up the warehouse because it is quite expensive and also the trips there when you need something

.. then I ask myself why this is not clearly communicated and the basement shows completely different spaces.

Storage room, wardrobe, and shoe cabinet combined in one in the house would hopefully be much more relaxed and tidier.

In terms of living space, we have also enlarged well through the two floors – from now 100 to 150-160 sqm.

You are currently making the big mistake that a) you apparently have not developed a room program for yourselves, b) don’t know your daily routine and never really played it through for the house multiple times, and c) do not know the soul (construction specification) of your property. Because if I count the bicycles in two years, then you will have 6 of them and won’t know where to put them because it simply was not planned. Regardless of whether a planner from a construction company or a freelance architect: they can only create a personally functioning house for you if you feed them with information. So you shouldn’t just sort the warehouse and basement but also yourselves. This includes measuring existing kitchen utensils and thus determining the number of cabinets. The same applies to wardrobe meters: a general recommendation is 50–60 cm width per person in wardrobe quality. If you orient yourself by that but the woman has a shoe fetish and collects handbags, you won’t be happy with 60 cm for your wife. She then takes your side too, and you will cause chaos with your things. Fifty more square meters of living space won’t bring you anything if it’s not where it’s needed or if you don’t even know how to use a partition wall. There are also walls that cannot be used as partition walls because a door is misplaced by 60 cm (e.g., bedroom door/wall parents). Maybe you also lack the enthusiasm to deal with this. But you are paying off the house for 30 years; that’s no bargain or small change, so if something doesn’t fit... so get to it. Go into planning, draw furniture, deal with the ergonomics of a kitchen, your actual and desired state, TV distance, and other standard measurements. And draw the potential house with bicycle storage, cars, etc. Make sure you can walk past the cars and that the parcel delivery person doesn’t scratch your cars. If you don’t have a site plan, then draw it yourself. And in the new building area, there is always information about the construction specification/Par34.