Are the deceased's children and grandchildren sinful if they keep his grave, which he built more than ten years before his death, at a length exceeding one and a half meters, as he instructed?

If the intended meaning of the grave's length is the length of the structure built upon it, then the man's children must remove the structure and leave the grave flat, level with the ground, or raised about a handspan. His will to leave the grave as it is should not be executed, as it violates Islamic law. Leaving the grave as it is does not benefit the deceased; rather, it may harm him if it is known that raising the grave to this extent contravenes the Sacred Law.