later inheritance in patchwork family

Caution! Marriage does not change the problem with the property. After the marriage, it still belongs solely to the partner, and if a house is built on it, that too.

However, he would inherit at least half if the partner dies. And if they get divorced (assuming community of accrued gains), he would also be entitled to half of the increase in value (and the house would be such an increase).
Yes, but all in all, this is really a case for a lawyer/notary and tax advisor.
Above all, the OP should be clear about what he wants. If he only wants to secure his daughter in the event of inheritance, as the thread title suggests, the situation may be different than if he also wants to protect his investment in the shared house.

However, he would inherit at least half if the partner dies. And if they divorce (assuming community of accrued gains), he would also be awarded at least half of the increase in value (and the house would be such).

And what does the daughter get from the house if he dies?
Marriage does not fix that, even if it partly brings certain regulations.
As already mentioned, there are several pitfalls here, so going to a notary or lawyer specializing in inheritance law would be the right thing to do.

Also, it is important to think carefully beforehand about what one actually wants.

And what does the daughter get from the house when he dies?

If he dies before his partner? Interesting question. Probably nothing. My sense of justice would say that here, too, the increase in value during the marriage would have to be determined and she would then have to "inherit" it.
But of course, we can't provide legal advice here. It's basically just brainstorming.

However, I would be very interested in further reports from the OP, since something similar awaits me from the other side.

We buy land and build a house (only I finance, only I am listed in the land register). Partner with a child from a previous relationship moves in and contributes work. Of course, I want to secure and treat the two fairly somehow.
However, we plan to get married. We also want to have children together.
And then it gets really interesting, for example if we both die in an accident:
- No children together yet: her child gets nothing, my parents and sisters inherit everything
- Children together: the older one (her child) inherits nothing, the joint children inherit everything
- My partner naturally thinks both cases are unfair. So do I. Ideally, I would adopt her child, but that’s off the table because the father is still in the picture.
And then there is, of course, the case of separation/divorce.
You don’t really want to think about such things, but you just have to. I always say, I trust my partner today, but I can’t speak for the person in the future.
So a visit to the lawyer/notary is on the agenda for us as well.

Best regards

Tolentino

My sense of justice would say that the increase in value during the marriage would have to be determined here as well, and she would then have to "inherit" it.

Fundamentally correct, but the problem is probably that he has paid off the house considerably, while the daughter only inherits half of the increase in value, if there is any at all. That's why I also said that just getting married doesn't help much.

And then it gets really interesting, for example if we both die in an accident:

You can break it down further:

- already married at that point?
- who dies first? It depends on the time. Sounds morbid but that's how it is. Some really awful situations have already arisen from this.

-> that's why you need to go to a notary. Even more important for patchwork families.

Basically correct, but the problem is probably that he has significantly paid off the house, while the daughter only inherits half of the value increase, if there is any at all.
That's why I also said that just getting married doesn't help much.

But the house is 100% value increase when considering land with house versus land without house. So, in case of doubt, he might even come out better if, for example, he contributed less than half to the financing...

- already married at that time?
- who dies first? It depends on the time. Sounds macabre but it's true. There have been some really messed-up situations because of that.

Well, in my example, I already assumed being married.
If not married, the matter is quite clear without a will.

-> therefore, off to the notary. Even more important for patchwork families.

Yes, exactly!