House Purchase - Complicated Situation

My mother would benefit in this scenario by being paid out directly and thus no longer having anything to do with the house, as she wishes.

The house value is determined, let's assume 600,000.
We buy it off for 400,000, the difference of 200,000 is to be considered as an advance inheritance.

My father buys a nice apartment for himself with the money (400,000 - 240,000 remaining debts = 160,000 / 2 = 80,000 for each parent) and his savings, ideally also worth around 200,000, which is directly promised to one of the siblings after his death. I think by now you can guess which sibling I mean (-:
According to his argument, the residential property would then also increase in value in the future, from which he would benefit again.

The third sibling is also guaranteed 200,000, at the latest upon inheritance, only then is the remaining estate divided by 3.
Of course, there is a risk here that upon inheritance, 200,000 from both parents may no longer be available.
I still have to figure out how this can be better regulated.
Unless maybe you have an idea? Maybe the money is paid by us brothers in case of emergency??

Which reliable agreement would you like to hear?

But I think it mainly reflects your own fears, no offense

Phew, it's quite interesting what kind of reactions this situation and possible decisions trigger in some users here and how emotionally charged many write.
One might almost think THEY have to decide themselves. From that perspective, I will now only address the factually important matters.
Still, thanks of course for the lively discussion.

Actually quite obvious – he built it himself and now does not want strangers living in it but prefers to pass it on to the direct descendants.
By the way, that is also a reason why I am looking for a solution in which we sooner or later become homeowners. The siblings have no interest in ever moving into the house.

That is correct.
However, she has no interest in the house anymore and would prefer to receive the present value in cash.
Therefore, a solution where we buy the house directly from her and pay her out would be to her advantage.

The father's wish is to pass the house on to the children.
Better like this?

That is not correct.
To put it bluntly, a house in downtown Munich would very likely continue to gain value or at least not decline in value even without major maintenance.

I see it the same way now.
The question now is how to realize this, since as mentioned we cannot buy the house completely at market value plus renovation costs.
My idea would be the following:

The house value is determined, let's say hypothetically 600,000.
We buy it for 400,000, the difference of 200,000 is to be considered an advance inheritance.

My father buys himself a nice apartment from the money (400,000 - 240,000 remaining debt = 160,000 / 2 = 80,000 for each parent) and his savings, ideally also worth around 200,000, which is directly assured to one of the siblings after his death. I think you can guess which sibling I mean by now (-:
According to his argument, the apartment property would also increase in value in the future, from which he would benefit again.

The third sibling is also assured 200,000, at the latest upon inheritance, only then the remaining inheritance is split by three.
Of course, there is a risk that at the time of inheritance there is no longer 200,000 from both parents.
How that can be arranged better, I still have to think about.
Unless you perhaps have an idea? Maybe the money could be paid by us brothers in an emergency??

My mother would benefit in this scenario by being paid out directly and thus would no longer have anything to do with the house, as she wishes.

see above