Nathan - Immortality, you can be killed, but you will be resurrected. The gap appeared to get smaller with each attempt. He survived a gunshot to the brain, metal spikes through his body etc. Unsure if this also retards aging. It recovers all injuries, when the user dies. In addition, the user can see and communicate with ghosts for up to 24 hours of their deaths and interact with them.
Curtis - time travel (to the past). Based on regret, so every time you really regret something you get a chance to rewind time. Can't do it consciously. Also, if you regret something then you may well keep going back (such as trying to break up with a girlfriend). Can work as a defense mechanism, say if someone runs in, kills your mate and then goes for you. Not if the attack is unexpected. It works by going into your body, so limited to your actions.
Kelly - telepathy (receiver). Can't transmit thoughts, mind control, hypnosis or anything else.
Aisha - sexual touch - doesn't matter about gender or sexuality. A touch will make the recipient feel insanely in lust with you. No control over it.
Simon - invisability, also makes the recipient inaudiable. It works by making people not conscious of him, not true invisability.
If the user is taking ecstasy, the power becomes inverted and automatic to an extent (don't do drugs kids). Time Travel can push you forward into the future, invisibility becomes desirability - EVERYONE notices you and desires you. Telepathy means you have to tell everyone your thoughts, sexual touch becomes repulsion. Immortality is just reversed and you can be killed.