How can I convince my landlord that he is wrong?

Questioner

I have been renting a room and partial use of part of the rest of the house since 1-2-2018, initially for one year. The contract was tacitly extended, and now I apparently rent for an indefinite period. The landlord (who also lives in Peru and the US) also lives here regularly for several months, as stated in the contract, and that is why the rent was low, namely € 400 per month (€ 280 rent plus € 120 electricity, gas and water. As of 28-2-2019 I pay € 425 and as of 28-2-2021 I pay € 450. Now he wants to increase it to € 500, because his wife thinks that € 450 is too low. Am I obliged to agree to this? The increase seems to me to be quite high in percentage terms. Are there standards for this? Do I also have to allow his wife to live here regularly? Only the landlord is mentioned in the contract.

Lawyer

The rent may be increased once a year unless sustainable improvements have been made (central heating/heat pump/insulation, new bathroom, kitchen/renovation)