We are DVC members so no advice on room discounts.
For nice dinners, the Four Seasons restaurants (Noe, Mina’s Fish house) outshine AmaAma. If they eat at Noe, they should request the two top tables by the koi ponds. La Hiki is open for lunch and breakfast - solid option for low key meals. For more casual food there are great options across the street - Meikiko cantina has great tacos and a margarita flight, Eggs n Things does a great breakfast. Monkeypod offers a nice change of pace from the resort but food is nothing special. Roy’s was underwhelming honestly so unless they just love Roy’s they should skip it. The non Disney restaurants can be booked on OpenTable. I would suggest they do the character breakfast at the resort - the food is good and it is one of those things you just have to do once.
I would suggest splurging on a cabana if they want to be by the pools. On our last trip we booked a cabana for two days and totally worth it.
The Aulani luau is fun if they’ve never been but it’s not something we’d do on every trip.
If they will have a car, Foodland is a grocery store with fresh poke etc: it’s in Kapolei. We always have a full kitchen so we stock up on drinks, snacks, breakfast items, etc. There’s a Costco and target also reasonably close in Kapolei. If they don’t need/want a ton of food/drinks for the room, the Island Market in Ko Olina is a great option but pricier than Foodland/target/costco.
Also, they should be aware on the return flights most airlines limit how early you can drop your luggage off. So, if they’re flight leaves at 5pm, they should not plan to check in/drop off luggage at 10am and then leave to do something else.