Purchase recommendation 2 condominiums in a 3-family house

Then you are lying to yourself, because the land value is included - it is considered with 0% return in your calculation. So the construction was economically nonsense.

The entire house is priced at 920k and that seems a bit too big for us..

Large numbers often have this effect. In the case of a rental property, if I may put it that way, the absolute purchase price must always be seen in relation to the rental income, which makes repayment enormously easier. The third party reduces the default risk, and sole ownership protects against a troublesome co-owner. As long as you keep some cash available to cover repair measures and to endure dealing with the misfortune of a late-paying tenant without financial trembling, it is quite possible that the purchase of 3 apartments would even be recommended by your banking partner. These are very general considerations, which of course cannot take your specific situation into account.

With 100k equity, I would still have to borrow €884,000 at (assumed) 3.8% interest, 1% repayment. The monthly rate would already be €3536..

There is a qualified rent index here, I ran through it yesterday (+allowed 10% deviation). For all 3 apartments, a monthly net cold rent of around €3400 could be achieved.

The property is supposed to cost €890k, 3.57% broker fee, 5% real estate transfer tax, 2% notary and land registry costs, so a total of about €984,000.

With €100k equity, I would still have to borrow €884,000 at (assumed) 3.8% interest, 1% repayment. The monthly installment would already be €3536..

With a gross yield of just over 4.5%

It is only 4.14% gross relative to the total investment costs of 984k. That is - for good locations - completely fine.