That's really horrible, thanks for taking care of him. I'm surprised you paid the woman, I would of just demanded she release the animal that she was abusing.
The first thing I would do is make sure the Alex is not near the Ekkie. You're gonna have to take it to the vet for a whole host of reasons- make sure there's not any communicable diseases, that it doesn't have any organ failure from a poor diet, if there's a medical condition for the feather chewing, etc.
In addition to health reasons, keeping the Alex away from the Ekkie will make sure it doesn't copy the Alex's noises. Honestly I think it's just going to take time for the Alex to quiet down. Birds that are abused like that have nothing but their own voices to entertain themselves with. It's a reason why a lot of abused shelter birds have amazing vocabularies.