A brother consumed a pirated product/game that itself by nature is haram. How should he make tawbah, must he pay the real owner of the game for his tawbah, must he estimate the amount of money and pay in sadaqah?

I am not sure in regards to your judgment that the game itself is forbidden. I understand you mean maybe it contains certain content. However, you cannot steal from people. Therefore, you should pay for the product that you have pirated.