Is the husband obligated to first buy the agreed-upon gold for his wife, or to send a monthly salary to his well-off parents?

If a husband sending money to his parents prevents him from fulfilling his promise to his wife, then he must prioritize her first, especially if his parents are not in need of the money. However, if sending money to his parents does not prevent him from fulfilling his promise, then there is more latitude in the matter. And a husband sending money to his well-off parents, if the money is surplus to his needs, is considered an act of maintaining kinship ties (silat al-rahim), and he will be rewarded for it.