On divorce, must the hantaran money and jewellery be returned?

The mahr is not returned (except in khulʿ), while hantaran and gifts depend on custom, agreement and the court's decision.
Hantaran money is a custom, not a pillar of marriage. Gifts that have been fully given (hibah) are in principle not asked back; the Prophet ﷺ censured those who take back their gifts. Jewellery bought together may count as jointly acquired matrimonial property.
If there is a dispute, the Syariah Court will assess the status of each item. Avoid reclaiming gifts in a humiliating way. See mahr.