I'm going with mixed feelings on this, and I've eaten at the Roy's in Ko Olina a couple times, as well as the one near us many times (Baltimore is our closest one right now).
The one at Ko Olina is on a golf course. While I love to eat outside at Ko Olina, it's always too cold and windy at this place. The prices are WAY higher than Roy's at our current home. The food is good, but last time we ate there, I was blown away at how much we spent (it was likely $400 for the 4 of us adults eating there). I'm not cheap, but it just was good not THAT good?
I have never seen this place full, so would not worry about making a reservation too far in advance. I'd just call that day and see what's good. Which is unusual yeah - for most places we make reservations, but this place is never booked that I've seen.
I'd see if the "nonadventurous" tween wants to just eat back at the resort really. For the time we went with friends, we all left our kids at the resort (the Marriott Ko Olina) to fend for themselves. They enjoyed it much more than going out to where they didn't feel like going! They hung out in our condo and I forget what they had - maybe we made something for them ahead of time like pizza I think.