What is the ruling of Islamic law regarding a wife's seizure of a car and her false claim of being coerced into selling it, and what is the ruling on her uncle and mother supporting her in this, and how valid is her statement that she has the right to use the car as long as she is under his marital bond, based on the Prophet's saying to Hind: "Take what is sufficient for you and your children in a reasonable manner"?

If the situation is as you described, then the wife is unjust for refusing to hand over the car after selling her share and receiving its price. Her family's approval of this is cooperation in sin. As for the wife's reliance on the story of Hind, that is specific to the permissibility of a woman taking her due maintenance from her husband's money without his knowledge if he does not spend on her in a conventional manner. She is not allowed to take anything from his money without his consent if he provides for her or if she is disobedient (nashiz).