My 2 cents as a dive instructor
I loved the hot girls. Some nice legs there. I thought the sharks looked very realistic. Well done!
BUT...
No diver would EVER go diving without fins. It's like driving a car with a 50cc engine. It's like trying to cross the Alps with only a Swiss army knife. It's beyond stupid. You have no power. So that was totally unrealistic. And not wearing fins out of fear to kick up dirt is also nonsense.
The constant water treading the girls were doing was nuts. It's the reason you wear a BCD (buoyance control device), you add/release just as much air as needed to stay neutrally buoyant. If you ever see someone diving who is constantly kicking their feet in order not to sink: they're beginners or just divers who'll never learn. Also when the group surfaced with the dad in the small cenote, they just should have put air in their BCD and they would have floated without any effort.
A tank being at 100% means sh*t. You want to know the unit. Divers normally dive with something like 220 bar or 3000 psi. Once you reach 50 bar or 700 psi you make your way to the surface.
If you're getting low on air the last thing you want to do is go deeper as you'll use even more air there. The smart thing for the girls would have been to find an exit that leads them higher, not deeper. At 47 meters depth the pressure of the air you breathe is 5.7 bar, at 20 meters depth the pressure is 3 bar, so about half of 5.7, giving you about twice the time remaining.
Nobody would ever go cave diving with just 1 tank.
The ONE thing you want to keep when diving is your cool. The moment you start panicking you start breathing an awful lot more and you suck your tank dry in minutes.