Joe, not sure Garden Island would qualify as a family resort. It's pretty remote and as for things to do other than diving, there's not much there.
My recollection is you get 2 boat dives in the package but that a 3rd dive and a night dive are offered for an additional fee. Should be easy enough to find out I suppose on that. It seemed if you instigated a sign up sheet and got the minimum, they did these extra dives.
As for the shore diving, that's a good name for it. It's so shallow that at times, my tank was out of the water. LOL! Well, almost. It took me a while to get someone at the resort to admit they have shore diving. It was like, Oh uh, talk to so and so about it. Finally, the head guy showed up and showed me where the tanks were and said just grab one and let the dive desk know you took a tank. Seems to me it was $5 and is probably discouraged so you'll do the extra boat dives. Diving from shore solo wasn't a problem. I was there with Eric, James, Tortuga for the Digital Shootout so, not sure if our diving was less restrictive but the DM's seemed fairly layed back to me. In fact they were good at finding critters so, you'd probably want to follow them off and on just to get some of the more unique things that are usually not seen.
Of course the main dive sites there are world class. Soft corals galore and quite a few macro subjects as well. Short boat rides. Currents can be killer. Keep towards the bottom of the reefs near the sand and it makes a big difference. I'd go back there myself so maybe that's the best I can say.
Rand