While non-resident visitors to the US are supposed to declare the value of all items that will remain in the United States, I would suggest going beyond just that and would suggest at least verbally mentioning the jewelry just to make sure it doesn't become a problem -- even if it may mean risk paying c. 6% or whatever the duty is nowadays on jewelry because of something rightfully or wrongfully concluded by the involved CBP employees.

If coming into an airport like JFK, EWR, ORD, IAD that is used to lots of South Asian visitors coming for weddings in the US, I'm sure they've encountered a lot of valuable jewelry coming in with the cabin baggage for wearing at weddings before heading out with the jewelry to go back home. But I'm also sure that at times they've encountered a lot of valuable jewelry coming in the same way but it was intended to be a gift or seen as intended to be a gift or commercial merchandise and that can be an issue. You don't want your parents to unexpectedly end up in the latter kind of group.