2 buyers - 1 property - different amounts of money - owner?

Otherwise: Simply have a GbR contract notarized before signing the purchase agreement and the GbR will become the buyer of the property.

Small addition: Presumably now eGbR

A finances alone ==> stupid if B also has co-ownership

He can only have co-ownership if a gift of the fractional shares takes place or previously from money. But that is not intended, as one wants to avoid the gift tax. The goal would even be to give 100% ownership to the one who pays almost nothing. But that would be too expensive because of the gift tax.

B finances alone ==> even worse, because A is the main owner

Same reason as above - gift tax too expensive.

A+B finance together ==> analogous to variant 2, because each borrower is personally liable for the entire debt

Both sign the financing application. Both are jointly and severally liable. But one would contribute significantly more to the installment. In that case, the one who contributes much less overall (because he provides less equity). That is also positive, as he can acquire more ownership without a gift.

How does it actually work?
1200€ installment - only one pays. Is the loan amount then credited to him as a share of ownership acquisition? Both sign the loan application - but only one pays (at least, if he does not default, then logically the other would have to step in).

Otherwise: Simply have a GbR contract notarized before signing the purchase contract and the GbR becomes the buyer of the property.

I had heard of that too. But then it becomes even more complicated with taxes. What if, for example, you want to deduct craftsman wage costs from your income tax declaration? That is then no longer possible because the property belongs to the eGbR.

What about the common child? Does it inherit the eGbR assets or the eGbR itself? Is there then a significantly higher inheritance tax than if the child would inherit the property like that?

Can you gift the property to your child? Surely no taxes would be due because the allowance is 400,000€. Gift from parent to child.

Both sign the financing application. Both are jointly liable for it. But one would contribute significantly more to the installment. In that case, the one who contributes much less overall (because they bring in less equity). That is also positive, as they can acquire more of the property without a donation.

How does it actually work?
1200€ installment – only one of the two pays. Is the loan amount then also attributed to him as a share of property acquisition? Both sign the loan application – but only one pays (in any case, if he defaults, the other would logically have to step in).

Both are borrowers. You cannot be "a little" pregnant. The bank does not care who pays. EVERYONE is personally liable for the full debt. The loan amount has nothing to do with ownership shares.

Apart from that, I read so much ignorance, half-knowledge, and "stupid" questions from you that I will first disengage until you have properly had yourself advised – yes, that costs money. There are many specialist lawyers for that. Everything else here in the forum makes no sense.

And I still do not understand the specific construct you have in mind. You should draw it out. A pays for the property, but B is supposed to become the owner? Huh?

He can only have co-ownership if there is a donation of the fractions or previously of money. But that is not intended, as one wants to avoid the gift tax. The goal would even be to give 100% ownership to the one who pays almost nothing. But that would be too expensive due to gift tax.

Confused thoughts, sorry.

The reason why Person A primarily pays for the property is that Person B has more money than Person A. However, Person A is supposed to have their main residence in the property. Therefore, Person A rents out their property to Person B for large fractions.

Do us and especially yourself a favor and go to a tax advisor or notary.

The reason why Person A mainly pays for the property is that Person B has more money than Person A. However, Person A is supposed to have their primary residence in the property. So Person A is essentially lending Person B their property in small fractions.

Read that again ... and then take the advice of to heart.