It's been over two decades since I read this story, so bear with me. There were three humans; two men and a woman, IIRC. Each had a psychic ability: clairvoyance, telepathy and telekinesis.
There was a war going on between humans and an alien race, a point which became important later in the story. The three are being sent back from the war due to their being unusable in the war. The ship they are on is attacked in space and they escape in an escape pod, landing on a primitive planet of humanoids.
They set up or join some kind of traveling performance where they do tricks based on their abilities, because they think they're stuck on the planet. Then the enemy aliens show up and they have to grow and learn to be able to fight them off.