Buying a house from grandma or waiting for the inheritance?

My mom cannot tell me whether she owns 2/3 or 1/2.
In any case, one house belongs to her and the other to my grandma + her house has the extension where I live as a tenant.
[..]
My dad has been putting pressure for years and wants clear conditions, but my mom is listed in the land register together with my grandma.
And both seem to simply look the other way in this matter.

How can someone not know what % they are listed with in the land register? Immediately get a new excerpt on Monday. If you consciously look away like that, there could still be surprises waiting, like the case where only the grandmother is actually listed. I really hope there isn’t something lurking in the dark like "We all agree, let’s save the notary fee." But based on your statements, I wouldn’t be sure about that :(

Apparently a lot was somehow done and fiddled with here and "it’s probably correct."

No… nothing is correct if you don’t even know yourself and are willing to clarify it. With that attitude, I also wouldn’t rely on an early inheritance being airtight. In the event of inheritance, it will suddenly be forgotten and everyone will want to be paid out. Forced auction then becomes inevitable and everyone loses their home.

I moved out at 19 and at 27 I moved into the semi-detached house (80m2 living space) and have been paying rent ever since. I was told that it would eventually be "mine." Which of course isn’t true and I was too naive.. actually downright stupid.

On the contrary. You were neither naive nor stupid back then, but did everything right: you are a tenant. Investment is not possible. Every euro that goes in goes to a larger joint inheritance community, of which you only have a very small share.

For the benefit of all involved, I still recommend requesting the land register excerpt and reviewing the inheritance waiver. Then you can see how to proceed. Also, the land division should be tackled. In my opinion, that would be well invested money.

If you can only "not quite follow" it, you are far ahead of me. By my own estimate, I understood at most an eighth.

Sorry, I find it difficult to explain all of that concisely and precisely, as I myself only understand half of it. Thank you for still trying to understand it.

Your answer: What I believe I have understood in summary is the following: 1. the OP lives in a house that is part of a complex, interconnected conglomerate. 2. the complexity of the conglomerate is only topped by that of the future community of heirs. 3. she wants to buy this house out of the conglomerate, and that before the grandmother’s death occurs. 4. the grandmother trusts that her foreseeable end of life will spare her from triggering this tense situation by addressing it.

Given the above summary, I would look for a property that a) has no connection with the described real estate conglomerate and b) is out of earshot of the explosion when the family "peace," which stands on shaky ground, is shattered by the inheritance case. Also, where the explosion is expected, according to the grandmother's assessment, within the next two years.

So actually you summarized it well, and I can “read” your smirk here so far :)

The very first point of contact/information source is the land register entry. I would strongly recommend obtaining the information BEFORE you bring yourself to safety before the crash. Everything else discussed is absolutely worthless when it comes to the property. WITH the land register entry, further steps can then be derived.

Actually, you summarized it well and I can "read" your smirking from here

I even literally "laughed out loud," exactly at this point:

She didn’t say "No," but wanted to ask her son. Which she hasn’t done for a year. Yesterday my dad asked if she had ever talked to him, and she said "No, I probably have at most 2 years left to live anyway."

Namely about the grandmother’s life experience, who probably has a pretty clear idea of the severity of the blast.

She’s afraid.
Afraid that we will push her out
Afraid of probably everything related to this.

I consider this a misinterpretation. In my opinion, the grandmother is simply acting wisely in life by extending the fuse or watering it until at the moment of the blast she is safely underground. So don’t be surprised if she explicitly requests in her will to be buried without her hearing aid.
She doesn’t need to fear for her own right of residence; that can be included in the purchase contract, which would even be beneficial for your tax situation regarding a possible combination of purchase, gift, and pre-inheritance. Also, there is the instrument of a legacy that the notary can explain to you.

But no matter how well or poorly one can defuse the problem in its explosive potential for family "peace," if you are looking for a solution for the described purchase project: my very clear royal recommendation remains to look for a property that has no contact whatsoever with the whole family (real estate) universe. So at most in the same location, but not even within sight of any of the family fence posts. The grandmother knows that after her comes the flood – or at least a fight and struggle that would make Cain and Abel look like a dream team in comparison.

In any case, one house belongs to her and the other to my grandmother + her house has the extension where I rent.

Exactly not! Your mother cannot own a house on an undivided property. All buildings on one property belong jointly to the first heirs; who owns which shares is recorded in the land register.

In the (unregulated) case of inheritance (then the number of owners of all houses will increase!) it will blow up terribly, so your parents are advised to look for something new now!

Exactly not! Your mother cannot own a house on an undivided property.

That's right, for details I recommend this (although long) story: our "pianist thread"

In (unregulated) inheritance cases (then the number of owners of all houses increases!) it will blow up terribly, so advise your parents to look for something new already now!

The problem of fragmentation is unfortunately not a "privilege" ;-) of unregulated inheritance cases.