M y family of 4 (age 8 &12) are headed to HI for first time. I need suggestions for a luau on either island. Old Lahaina is sold out so looking at Feast of Lele or Smith's but would welcome feedback. Also would love recommendations for restaurants. We are staying at Koa Kea in Kauai and Fairmont in Maui but willing to drive. We like more casual than fancy, local, nice ambiance (outdoor/ocean view). Also would love a couple must dos. We like hiking, snorkeling/boating, exploring. Also love live music.

Also spending 2 days on Oahu to see Pearl Harbor. Do we need to book tickets ahead of time? Any suggestions for restaurants in Waikiki?

For Kauai, take a look at my trip report from last year: Kathie & Cheryl's notes from Kauai 2017 lots of info on restaurants.

I would look at luau at the Sheroton Kanapali-Experience Sheraton Maui's own luau. Located beachfront on Kaanapali Beach, the Maui Nui Luau shares the music, dance, and history of Hawaii's islands right here at the foot of the famous cliff diving point, Pu'u Keka'a-http://www.sheraton-maui.com/dining-in-maui. Or Drums Of The Pacific-http://drumsofthepacificmaui.com/.

On Kauai, be sure and take a boat trip to see the Na Pali coast, absolutely beautiful. I like the morning trips better as the seas are calmer. Not a big luau fan (been to 2) but Smith's on Kauai has a "show only" option for $15pp. I would be tempted to do that and spend the money on a nice dinner elsewhere.
Maui is supposed to have the better luaus and I believe you can get on a waiting list for OLL.

I can't recommend driving an hour from Wailea to Lahaina and back at night along the pali. Both Grand Wailea and Marriott Beach Resort have nice luau entertainment. (You can even save on the GW one with a Costco coupon.)

There are a few nice restaurants at Shops At Wailea. Go north five minutes into south and central Kihei for casual -- fish tacos, plates, etc. at Maui Taco, Coconut's, Paia Fish Market (Kihei Branch). Nalu is nice -- talk about casual, the post office and Ace Hardware are right *there*. LOL Above Wailea is Gannon's -- panoramic view from a golf course clubhouse venue. Five Palms at the Mana Kai in South Kihei has outdoor seating on pretty Keawakapu Beach. Sarento's is 'upscale Italian' on the same beach, in behind the Day's Inn.
The Kamaole Beach Parks have free parking, lawns, shade, picnic benches, rest rooms, showers -- and lifeguards.

You can book the Navy tour to the Arizona, but they are currently unable to land on the memorial until extensive repairs are made to the landing pier. I think it's still worth seeing the movie and going out on the boat. You could spend all day at the Missouri and other exhibits -- at least our DS and DGS did!