Sounds like a great plan, but don't get too tied to making plans. Sometimes time seems to slip away, and you end up spending much more time than you anticipate just sitting in a chair enjoying the scenery!
An idea that may occupy the kids and adults both: bowling at Fido's Sandbar. It may be the furthest bar/restaurant south (about 2 miles S of town?). It has 2 bowling lanes right on the beach. After you order, the kids can bowl a few rounds. It is not necessarily what I call local cuisine, but they tend to have a decent selection on the menu, a weekend barbeque and great drinks. And, there is a pool to cool of in if you get hot. We enjoy it. Check out Fido's in town for live music and a place to hang out while the girls shop.
I think the reef fishing is popular, and it seems like that is the place for snapper, etc, that you would cook yourself. The guide usually cuts the fish up, and you can either buy the cooking ingredients yourself or contact Simon on this board to deliver them before you arrive (and have the beer in the fridge and cold for you upon arrival).
Definitely do Hol Chan. We use Suya, a tour company located about 2.5 miles south. If possible, try to schedule a morning when the fishermen are out. We spent a whole morning (when we only paid for a 2-hr snorkel) tied to a fishing boat that was cleaning their catch and throwing the scraps in the water. We swam with more nurse sharks and sting rays than we could count, plus a huge sea turtle!
I can't comment on the ruins/zip line/cave tubing, as we have yet to make it off of the island!
For local cuisine and seafood cooked lots of ways, go to The Reef Restaurant. For the kids, all the pizza we've had has been good. Everyone has their favorites, but Caramba's, El Patio, Caliente and Mangos are all good for burritos, seafood, chicken, etc. for either lunch or dinner.