What is the Sharia ruling on demanding payment of a car tax for a car imported in the questioner's name, while his brother used it and registered it in his wife's name, and the brother refuses to pay, knowing that the debt is accumulating and preventing the questioner from disposing of his property?

Your brother is responsible for paying the amount because he owns the car, and he registered it in your name to facilitate legal procedures. You should explain to him the harm you are incurring and the increased taxes due to his delay, and that he should try to invalidate what is baseless. Seek help from those who have influence over him to convince him. You should not boycott him unless it becomes a necessary means to remove the harm. Rather, deal with him with gentleness and kindness so that he fulfills his obligations.