We are a family of 4 people, with 2 girls aged 11 and 7. We felt that the crew had a lot of experience. They took the security very seriously. The instructions were clear and fine - although I can imagine that the people in the back couldn't hear them. We were 80 people on the boat. We thought that it may be too much at the beginning, but it was actually fine.
As far as the snorkelling is concerned, it was fine. I even see a sharkš. But remember that it is in the middle of the "ocean" and there are quite some waves. My husband, who is not a great swimmer, and my 7-years old daughter, who actually is a good swimmer in a swimming-pool, didn't feel comfortable in the water because of the waves. Still, they saw a few fish and were happy with the trip.
We had a good time altogether and recommend it.