Is the questioner sinful because his brother failed to pay the rent for the apartment which was in the latter's name, and they shared its rent, after the questioner advised him to come to Europe and leave the apartment, knowing that the questioner cannot pay on behalf of his brother, and he feels guilty?

Your mere residence with your brother and your participation in paying the rent for the apartment he leased does not make you a party to the contract with the landlord. This becomes even clearer by your leaving his residence and emigrating from the country, while your brother continued to reside in the apartment. Therefore, nothing of the overdue rent is your responsibility.