Does sin befall a driver who transports foreign employees carrying alcohol in his car, even though he does not carry it with his hand?

Your work as a driver transporting employees is permissible, and the contract is based on this, not on carrying alcohol. Therefore, the sin of carrying alcohol is on the one who carries it, and there is nothing upon you as long as you do not assist them in carrying it and you express your disapproval of their drinking it. You should also invite them to Islam using da'wah methods specifically for non-Muslims.