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

Thank you very much for the interesting hints and comments.

Loans are to be taxed at 5.5%, that would be the worst solution. Then it would be better to take out a higher loan from the bank at 3.85%.

Complete nonsense. In contract design, you are basically free as long as it is reasonably arm's length.
I believe the 5.5% results from a ruling concerning an interest-free loan without a fixed term. There, the interest rate was applied for discounting.

You are completely getting lost with your half-knowledge.

Loans are taxable at 5.5%, that would be the worst solution. Then it would be better to take a higher loan from the bank at 3.85%.

Nonsense. It has already been written like that.

No rental income should arise, which would then have to be taxed again. It should be kept as simple as possible from a tax perspective.

Then don’t call it rent, but compensation for use.

Okay, I didn’t know that. But in the second step, the tax office is of course interested. If person B pays half of the property taxes, then person B gifts money to person A, which would trigger gift tax. At least from €20,000. But you want to avoid keeping track of all that. So everyone pays their share of the property taxes to the tax office proportionally to their shares.

No, the tax office does not ask about any of these things. You simply have no idea.

So person C must first have concluded a purchase contract with e.g. person B. Then this must be presented to person B and person B can then say that person A pays the amount? Couldn’t person B, if they want to annoy person A, set an unrealistically high amount in the purchase contract?

B sells to C. A can join the purchase contract or not. No, you cannot annoy A, because C must also pay the purchase price. B then has to pay tax on the profit from the transaction and A just laughs.

Exactly, the loan is then not credited 50/50 because it is assumed that only person B is repaying. Thus, person B receives the entire loan amount as shares. So this is agreed in advance in the purchase contract concerning the property—not afterwards. Otherwise, a notary would be necessary each time, logically.

Do you actually realize what nonsense you are writing?

We hadn’t even thought about a right of residence yet—would rent then be due (which we want to avoid). We would grant both a lifelong right of residence. It is not mandatory to live there, right? Or would that then be a second residence if, for example, person A lives elsewhere but also has a right of residence in the property?

A right of residence is only a right of residence if you actually live there. Then no rent is due (unless agreed otherwise). The obligation to live there does exist. Otherwise, the right of residence is simply deleted. As said, financing is then not possible.

I’m out. I no longer want to read such nonsense combined with ignorance and resistance to advice.

Just go to the tax advisor.

It is supposed to be kept as simple as possible for tax purposes.

Aha. To make it as simple as possible, you make it as complicated as possible. Not only I can't keep up with that. Most of what you think you know about possible taxes to be paid is wrong. You think a convoluted path leads through a thicket that doesn't even exist. I neither find the starting point difficult, nor are there no simple solutions for it. These have been mentioned.