So glad you adopted them.. man those pictures *shuddering* & they even get to stay together in their new home!! Congrats!
It wasn't too long ago I was in your shoes with a newly rescueCAG & feeling very overwhelmed so you are not alone. Gracie barbered feathers & has & will occasionally pluck tail/wing & back feathers. She was pretty bitey & didn't like woman. Had a bad diet, bad health etc.
So the first thing I'm gonna say is ... relax & breath - it's gonna be a marathon not a sprint
You've handled the immediate needs, they are in a safe loving environment, warm, clean & belly's full with no immediate medical emergencies.
I can recall feeling such pressure (self-induced) that made me feel like I had to resolve all of the behavioral/handling/eating etc. issues right away - quickly. Fact of the matter is once I lost my expectations, set aside any disappointment when we didn't make progress & stopped feeling like she didn't "like" me that's when the everything started actually coming together. I celebrated the small steps or big leaps and just learned from anything that didn't work. In no time at all we were buds.
Fear of the beak or lack of confidence - that's a hard one but parrots bite & you're gonna get bit. I opted the route of just taking the bites, didn't react except to say "easy - gentle" & grasp her beak from the sides to jiggle her loose, I always kept a favorite treat and toy with me to distract her while I returned her to a perch if need be. I also tried the earthquake technique (be careful tho - she may hold on more to avoid being unsteady). I figured the only way I was gonna have the opportunity to correct/redirect the behavior was when it happened so bites where inevidable.
Gracie will not let anyone handle her even now if they approach her hesitantly. If someone walks up to her says step up & follows with "easy" when she starts to steady herself IF they are confident she goes to them without incident. If not - whammo she'll lunge bite.
She absolutely measures a person up .. even if she knows them already.
Before I even attempted handling I did spend lots of time talking, singing, playing etc. with her. She was at that time extremely underweight so in the beginning she treats worked to start bonding.
To get Gracie to step up I did try a perch rather than hand but she is terrified of any sticks/brooms perches that are in someones hand - she's ok if they aren't being held. So this is when I realized I was gonna hafta take the bites to work with her.
I would keep a treat in one hand closer to my chest (making sure she could see it) with my step up hand extended, I'd ask her to "cmere" & "step up" (basically she had to stretch, touching my hand in order to get the treat) whenever she reached her foot towards me I gave a treat, when she advanced to touching my hand - treat, stepping up - treat etc. Once she would step up I used nuts as treats since it really kept her beak occupied longer.
Head scritches were ok with Gracie from minute 1 so I also used that as a "treat"
I'd get her to lower her head and while scritches I would offer "step up" & my other hand.
Gracie advanced super quick with me for handling - she wanted out of the cage & the only way I allowed her to leave in the beginning was by my hand. I used her wanting to get out as a form of "treat" the minute she stepped up I took her immediately to her favorite perch and made no further demands - none - little by little I took longer to get there & talked to her more when I did it. I'd reassured her constantly "wanna go over there?" , "you're ok, let's go get your toys" "easy Gracie" " Here we go ..weee" etc. I'd also encourage her to flap her wings & "fly" to the perch while still grasping my finger with the accompanying "wee" "fly Gracie" etc. All positive tone of voice.
Plucking - is a hard one. Gracie plucked/plucks damaged feathers but sometimes she's the one doing the damaging so eventually that will lead to her plucking the feather she previously barbered.
The plan the vet & I decided on.
Daily showers - she takes them with me in the morning, waits on the curtain rod when I'm done I bring her down to play. If I put her in alone she sometimes gets anxious & she doesn't play as much in the water.
On hot/itchy/dry days - she gets a misting in the afternoon or a full on shower if she decides to venture in & ask for one. Misting every few days I mix 100% aloe.
Healthy balanced diet
Direct natural sunlight (not thru glass or by artificial light - although she has one of those also). She goes outside in her travel cage several times a day (this is where she usually takes her afternoon misting), morning is a more direct sun afternoon is shady time usually. She has the option half of the cage is in shade/ half in sun. A minimum of 2-3 hrs a day. This is also to help with her other health issues.
Gracie has some triggers to her barbering so I watch for them & trying to prevent it before it happens.
She doesn't like to be completely alone in the house with 2 teens she usually isn't. Being locked up in her cage during the day/evening - unless it's bedtime - she's free reign.
Overpreening - she a preening freak & that is a prime time for her to decide to trim (barber) her feathers. I pay attention to her preening - if I start to see her getting that aggressive preen going on I'll distract her with a treat, toy, music or take her for some outside time.
Boredom - she has a lot to do just sometimes she doesn't wanna do it alone so I get her interested in an activity if I can't interact with her at that time (outside time, new foraging toy, shredding etc.)
Loud noises/yelling etc. - she hates it even if it isn't us doing it - if it's in a movie etc. she gets upset clearly she's lived in a fighting violent household at some point - we avoid the types we've learned scare her a lot.
She doesn't mind loud music, action movies etc. - it's mostly fight scenes/yelling/arguing that upset her.
Avoid any lotions or anything on your hands or the environment that may transfer to the feathers triggering a response.
Grey's sometimes have to be encouraged to get the blood moving so to speak or they'll laze around.
Lazing around/ idle beaks = preening/plucking/barbering etc. Get em engages & interested in something so they don't fixate.
Of course everything got a bit easier too once our avian vet was able to pinpoint her health issues & treat accordingly. No one wants to be handles or messed with if they aren't feeling well. So many issues can only be detected with bloodwork, fecal, testing etc. I would strongly urge getting them in to get some medical insights. I'd document anything you know about their past, husbandry etc. or anything you've noticed out of the ordinary no matter how odd or silly.. it may well help the vet determine what to recommend for testing or what you can do at home.
Sorry I was so long winded, it was a rough night - Gracie was stressed over the fireworks & she yanked out a tail feather last night right in front of me so I guess I'm a tad raw & questioning everything I do.
I can't help with macaws - but I'd suggest reading everything you can find in the forum by Birdman - he's like a macaw whisperer lol
Good luck & blessings to you for stepping up & taking on not 1 but 2 babies so desperately in need of a loving home.
It may take time but don't give up - it's possible