Hi, yes sorry to be the bearer of bad news but this is indeed what green cheek conures do.
Mainly this is probably to do with sexual maturity or breeding seasons but without knowing more details I cant say this is definitely it.
I dont believe in ranks/height dominance etc with birds, its more to do with who is the favorite person and how people react to the bites and generally behave around the bird.
Now for the good news, you can get your sweet cuddly bird back but its going to take time and patience to ride out the storm. It also means you need to show a non-reaction to any upsetting behaviours such as the biting, any reaction at all can re-inforce the biting and make a temporary problem one that never goes away.
Everyone handling the bird needs to know not to yell or tell the bird "no" "bad bird" or anything else
they need to know not to jump away from a bite, if the bird latches on though they can use their hand to remove the birds beak though. Ollie used to bite and really chomp down hard and chew....
Also once the green cheeks go off on one they tend to chase anything that moves so whilst your trying to stop him/her biting one hand the other hand is suddenly the target, so if he gets super agressive like that with his tail all fanned out etc then just tip him off you gently and walk away, if he flies after you, tip him off again (do not do the tipping if he is a nervous bird, it can make things worse).
Occassionally a Green cheek will bite because it doesn't like what you are doing and wants to be left alone, its up to you to get familiar enough with his body language to identify when your green cheeks getting uncomfortable and back off before it bites.
I can assure you that things will get better but like I said you need time, patience and quite possibly a bit of blood loss before things will improve. Always act confident, these guys can sense nervousness or upset. You also really need to pay close attention to body language, it takes a while to learn as these guys appear to change moods in a split second but they do give subtle warning signs and it will soon become second nature.
If you have any questions feel free to ask
