Double costs for the bathroom / who has to pay?

Content-wise, I can't contribute much but briefly on the differentiation of terms:

Bauträger:
You buy the entire plot of land and house from the Bauträger. One price.
As a result, you don't have to worry about the individual craftsmen. Your contact person is the Bauträger.

Bauunternehmer, Generalunternehmer, Generalübernehmer - BU/GU/GÜ:

You have a plot of land (or buy it from a private person, municipality, or elsewhere) and look for a company to build a house on it for you. Contracts can vary here. Sometimes you deal directly with the craftsmen in individual trades (also by agreement), or sometimes you do not.

Your version sounds more like BU/GU/GÜ. Now for me, it depends on how it is contractually agreed. You can post the relevant part of the contract here.

You won't get any legally binding answer (-> lawyer) but maybe opinions. With the information so far, it can't really be answered.

Well, your construction company has to pay the base price... But you already paid in advance for all the special requests (why the hell are you doing that????). You will most likely end up stuck with the costs, the construction company has nothing to do with that.

It is quite normal to settle special requests, or anything beyond the construction company's standard, directly with the respective trade, the construction company is initially hardly involved.

For clarification: you probably have a general contractor. A property developer always sells a house in combination with the land.

Learn: Never pay everything in advance!

Strange constellation that the developer apparently prescribed the bathroom companies with which you settled directly. What the developer provides, you also have to pay for. So if the developer now builds the bathroom for you after all, it of course costs. The money you paid to companies that went bankrupt is gone if they were also your contract partners.

I believe this is not a developer, right?

You can buy houses from a developer and at the same time award services independently. Especially floor coverings, painting work, and bathrooms are part of this, as these are done when the developer is already finished and can issue his final invoice. This is often seen in townhouse settlements or other areas that are uniformly developed by a developer according to an agreed pattern with the city. But this doesn't help the OP either.

Well, your construction company has to pay the base price... But you already paid for all the special requests upfront (why the hell are you doing that????). You will most likely be stuck with those costs; that has nothing to do with your construction company.

It is quite normal to settle special requests, or anything beyond the construction company's standard, directly with the respective trade; the construction company initially has little to do with that.

To clarify the terms: you most likely have a general contractor. A developer always sells a house combined with the land.

Lesson: Never pay everything in advance!

That’s exactly what we did. Bought a plot with a house. That definitely involves a developer. All other trades, except for non-contract relevant trades, were commissioned by him. So we had nothing to do with that. Probably just the bathroom, because we had special requests.

The prepayment was agreed upon with the developer. We were probably really too naive and gullible.

It will likely end up with us having to sue the bankrupt craftsman, hoping to get something back.

Maybe I just didn’t understand it correctly: what exactly was the reason for your transfer to the company that is doing the bathroom? Was the reason solely your special requests, or was it for the payment of the entire bathroom? The latter would be really very unusual.

is of course right about the "extra trades" even with property developers. But honestly, I didn’t fully understand the question either. Why is the developer charging you for something? The additional services/samples are clearly your matter but are also paid directly to the trade. However, advance payments are obviously not smart. Only if the agreed basic installation isn’t finished because the craftsman becomes insolvent should that not concern you. But as I said... just an amateur opinion and the contract details play a crucial role.