Having all these abilities why didn't they...

Bobby was a teenager whose powers were still developing. You saw the speed at which he was able to construct an ice barrier in the mansion hallway. He in no way was strong enough to do anything to stop the flow of that much water.

Xavier has no telekinetic powers in the movies (and only minimal ones in the comics). He only has telepathic powers. Jean is the one with both, so Xavier couldn't do anything at all to the water except stare at it from his wheelchair.

The kids were kids and like Bobby they were unlikely to have reached their full potential. Further, they were able to be locked up in a room, which should tell you all you need to know about their strength level and how useless their powers would be either in fighting that much water or escaping from it.

Nevertheless, you had Jones whose power allowed him to control electrical devices and made it so he never needed sleep. You had Arthur Maddicks who had a reptilian tongue in the movies and in the comics can project holograms with his thoughts and has limited telepathic abilities (not telekinetic). Then you had Jubilee who basically can shoot fireworks (explosive energy) from her hands. None of them could do a thing in that situation, even at full strength. The others are unknown to us but, again, room + trapped + underpowered children suggests across the board uselessness in that situation.

For Storm: She is weaker in the movies than she is in the comics. In the movies, her ability to generate directed wind was never shown to be powerful enough to counter nearly as much force as they were up against. She also lacks some of the powers her comic book counterpart might have used in that situation.

Lastly, Nightcrawler's teleport range in the movies is unclear and in the comics the more matter he tries to bring with him the less distance he can go and the more tired it makes him. If that holds true for the movies he likely wouldn't have been able to get everyone to safety in time so using him in the way you describe to escape the situation would entail sacrificing some of them.

However, many other people have also pointed out that he should have been able to make a play for Jean after she lifted the jet into the air. He had her in his line of sight and she didn't immediately go under. That I would concur with.

Or a better argument might be, why didn't they try to escape to the OTHER side of the dam, given they knew it was ruptured?