There is great info here and taking basic precautions go a long way. One thing I did want to say is that most likely your family
will dive below the waterline in mask, snorkel and fins, and forget to be scared. It is so beautiful one forgets to be scared. I know when I've encountered things like a bull shark, it is so amazingly beautiful and graceful and well just plain spectacular.
I marvel and the fear is there but it is totally eclipse by the beauty-it is worth it. Don't get me wrong I don't try to kiss the bull or follow him, just let him pass, make sure he doesn't turn around for another looksy and thank God for showing me such a spectacular creature.
You guys are going to have a blast!