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

That was a typo. It should be: The reason why Person A mainly pays for the property is that Person A has more money than Person B. However, Person B is supposed to have their main residence in the property. Person A therefore lends Person B their property for large fractions.

That was a typo. It should read like this:
The reason why Person A mainly pays for the property is that Person A has more money than Person B. However, Person B is supposed to have their main residence in the property. So Person A lends Person B their property in large fractions.

Stop. Back to the beginning. Please explain the situation from the start. Completely. By the way, you cannot lend a property. You rent it, use it, live in it - but you do not lend it.

Person A & Person B live in separate apartments. Person A and Person B (not married) decide to buy a property. Person B is to have their main residence in this property and gives up their current apartment for this purpose. Person A brings a lot of equity. Person B brings little equity. Person A wants Person B to live in the property rent-free (but this is then a loan -> The BGH ruled again in a recent decision (27.1.2016 – XII ZR 33/15) that in the case of a gratuitous transfer of use of residential and/or commercial premises, there is no gift, but only a loan.). And since Person A owns more of the property than Person B, Person A is basically lending Person B the remaining part of the property. However, Person A lives elsewhere. Person B then makes the property their main residence (their only residence).

That was a typo. It should read: The reason why Person A mainly pays for the property is that Person A has more money than Person B. However, Person B is supposed to have their main residence in the property. Person A therefore lends Person B their property to large fractions.

Person A and Person B (not married) decide to buy a property.

You know what? The only problem lies in your way of thinking. You calculate, for you there is only a partial pregnancy. This has nothing to do with partnership. Either you do it together or you alone. Decide. A house is a forerunner, a next step - either alone or a further step into togetherness. I already gave the advice to have a conversation with a notary. I don’t understand why this is not being followed up.

Person A & Person B live in separate apartments. Person A and Person B (not married) decide to buy a property. Person B is to have their main residence there and gives up their current apartment. Person A brings a lot of equity. Person B brings little equity. Person A wants to let Person B live in the property rent-free (this is then a loan -> The BGH ruled again in a recent decision (27.1.2016 – XII ZR 33/15) that in the case of gratuitous use of residential and/or commercial premises, it is not a gift but only a loan). And since Person A owns more of the property than Person B, Person A is basically lending the rest of the property to Person B. However, Person A lives elsewhere. Person B then makes the property their main residence (their only residence).

Then Person A buys the apartment completely and lets Person B use it free of charge. Problem solved. If desired, Person B can also acquire a co-ownership share.

You know what? The only problem lies in your way of thinking. You calculate; for you, there is only a partial pregnancy.
That has nothing to do with partnership.
Either you work together or you go alone. Decide.
A house is a trailblazer, a next step - either alone or a further step into togetherness.
I already gave the advice to have a conversation with a notary. I don’t understand why this is not being followed up on.

Apparently, this is not about partnership if you read his post 21.
And a notary does not provide tax advice.