Sorry I can't speak to the parasailing and snuba, suggest you do an online search for that.
Three good family beaches are Maegens Bay, Coki Beach and Saphire Beach.
Maegens is by far the most popular and therefore most crowded. It is an excellent family beach with food, rentals and facilities. Besides Cab Fare there is a small admission fee. Snorkelling is not good here, but the beach is fabulous.
Coki Beach is located next to Coral World a popular paid attraction. Coki is a family oriented beach with facilities, food (cheaper than Maegens and better too) rentals and decent walk in off the beach snorkelling. There is a vendor running scuba off the beach as well.
Saphire has full facilities, food and rentals and has ok off the beach snorkelling.
Coki and Saphire have no admission fees.
We visited Saphire Beach this past Thursday and it was Excellent. Our cab driver suggested it above Coki telling us it was more secure and more private. AKA less crowded. We got there around 11am and stayed until 2:30pm, I would say at the most there was 30 people there at any given time. The beach is free, there is a small welcome center that sells water and snacks. There are excellent bathrooms and I think lockers. Showers are available as well. There is a nice restraunt on the beach too and the views are to die for. There is really good snorkeling if your looking out towards the water to the left... towards the jetty. You can see the reef right on the beach line... if you swim out though near the middle or end of the jetty its about 10-15 feet deep in some spots and the reef is 4-6 feet high. There are urchins the size of basketballs, huge parrotfish, damsels, wrass, goby, sting rays, trunk fish, the list goes on and on. They have gear for rent there, although we had our own so I don't know how much it is. The cab fare here is $8.00 pp however the taxi driver we had gave us a tour of the island with many stops for only $20.oo pp.
Here are just two of my photos, not the best ones but something to show you...