Bird help????????????

I do not know about the disease or if a bird can stay sick for two years unless it recently got sick. There are some diseases that YOU can get from a bird or a dog though. Once birds get sick they get sicker fast. You could try taking it to a vet or at least calling one. It sounds like to me that the bird may not be getting much to eat or drink. I think you should separate the birds in two different cages so Luna will get something to eat. Scout may love to hog the food but that cannot be healthy for Luna. How did it lose its tail feathers? Did you ever think that maybe Scout is bullying Luna? If Luna is molting does it have pin feathers on the top of its head (pointy feathers). Maybe it needs molting food. Luna is seven years old-which is an old bird. So maybe it is sick/poor nutrition. I hope I helped!