I suspected coccidiosis or worms. More likely worms.
I had a worm outbreak once. It was terrible. Birds couldn't fly and were dying. I treated the worms by giving 2 cc of
Ivermectin per gallon of water. Yes, it's a cattle and swine injectable. I wouldn't recommend it unless it worked. And it did. Keep it out of the sun, as it loses its beneficial qualities. Don't do more than 2 cc.
Do you give anything through their water? I like giving
This to my birds. As well as probiotics for them. Do these once a week. I also add Apple cider vinegar to their water once a day. I do a tablespoon per gallon. this is just to keep them healthy. It won't get your bird better.
Do they have grit?
I hope this helps.