Buying a house without equity at a relatively young age

Buying a house and renting it out makes little sense with the increased interest rates. Let's assume an investment of 500k (purchase price, incidental costs, and minor cosmetic repairs), which alone results in 20k interest costs (at 4%) without maintenance reserves. To make this cash-flow neutral, the cold rent would have to be easily 2,000 euros. The OP would have to pay that as well if buying (plus repayment). But he is willing to pay a non-rational lover's price to "own" it.

A financed real estate investment only makes sense currently if one expects future price increases. If one looks only at the ongoing income, one is committing pure stupidity. The owner-occupier at least enjoys consuming a large living space. And the speculation on price increases can only be realized by the OP if he buys it himself. Otherwise, he might only get this income as a sole heir, but even then, his wife would have nothing from it.

With 2,000 euros (or even more with renovation backlog) cold rent, the OP would probably quickly give up on the house and prefer a 2-3 room apartment appropriate for old age.

Now you have forgotten that it is about family. So it is basically also property, he receives it when it is paid off.

Rental income must also be taxed, the saved rent does not. Obviously, as long as you have interest costs and depreciation, it doesn't matter. But with the currently unattractive price-interest ratio, buying only makes sense if you expect inflation and rent increases. At the latest then, you will eventually have to pay taxes on your rental income (unless you arrange it illegally within the family under the table).

If parents want to do something good for their children, it's better to do so via a direct equity injection or joint liability with a good relationship. The rental construct is a relic of the zero-interest phase. Today it is no longer really sensible.