1) Should they actually have Blindsense?
2) I think you meant the shriek attack to target Will, not Wisdom. There was also a labeling error in the Ultrasonic Screech description. It should instead say, "You can use Ultrasonic Screech as an encounter power."
Blindsight / sense is better, but I initially wanted to only include descriptions from the PHB. Given that players might not have access to the MM. The thing to do I suppose is define 'Echosense' within the document but at this stage I'm adverse to adding new rules.
You're definitely right about point 2 - No idea where Will came from!