1. Eldar codex psychic powers have their own rules covered in the codex, one being not requiring line of sight for some. Ones that require a target still need LOS just like a shooting attack.
Standard book psychic power require LOS if the power has a target and cannot be use through a fire point on a vehicle, the exception being a PSA that is treated as an assault weapon and can be.
2. Disembarking does not remove the effects of crew shaken or stunned from the models that were embarked. So passengers that are "crew stunned" can not fire in their next shooting phase regardless of disembarking or not. This does however not stop them from using psychic power only PSAs.
I'm so used to the Eldar powers not needing LOS i had to go recheck the whole thing page 67 is quite clear after all, here have some Rep.
The Eldar, more than any other army, should not only look at the output of each unit individually, but the synergy of multiple units together and their role in the force as a whole. - Fable