Setting conditions for property sale - How to secure them?

Good morning,

my parents would like to sell a plot of land to a prospective buyer. Since they themselves are interested in ensuring that the plot is not excessively developed in the future, they would like to contractually stipulate this.

More precisely, it is about fixing the maximum height of the development and type (max. single-family house with a self-contained apartment (the gross floor area would then probably have to be determined)).
The plot is basically subject to §34 of the Building Code, but there are restrictions from the city due to a building inquiry. According to the building inquiry, a maximum of 2 single-family houses each with a self-contained apartment OR 2 semi-detached houses are allowed.

The prospective buyer has basically agreed to my parents' conditions. However, we have heard that although this could basically be recorded in a purchase contract, it would not be protected against potential straw men. If the buyer were to resell the plot, these arrangements would no longer have to be observed.

Is there a way to make this irrevocably fixed?
Could something like this be entered in the land register, or what other options would there be?

Thank you very much!

In our purchase agreement, rights have been granted that we must also transfer to subsequent owners by contract. In principle, this therefore seems possible.

The question for me would be whether such a restriction, as you would like it, is even permissible and what realistically happens if it is violated.
That is the task of the notary.

It was similar for us. You can have something like that registered in the land register. That then reduces any possible resale value, but it can be done easily through the notary.

Thank you all!

That was the hope, to be able to establish something like that permanently with a land register entry. Since my parents want to get a lawyer involved anyway to handle everything smoothly, nothing should stand in the way of that.

Thanks to you all!

That was the hope, to be able to establish something like that permanently with a land register entry. Since my parents want to get a lawyer on their side anyway to handle everything smoothly, nothing should stand in the way of that.

They should do that and always remember that they will have to go the difficult path if the buyer violates it. The land register is just an old dusty file and people tend to change their opinions.