Do those who work in a management consulting office sin when they provide feasibility studies for projects, if the owners of these projects later obtain usurious loans, knowing that the office advises them to turn to Islamic banks or non-usurious government funds?

If the feasibility study has no bearing on the project owner's choice of financiers, and you are guiding him to Islamic banks, then there is no harm in your work. However, if you are certain or highly suspect that he will deal with interest-based banks based on your study, then it is not permissible for you to assist him, due to Allah's saying: "And do not cooperate in sin and aggression."