Aggressive biting / Territorial?

[Grim]

Hi all, in the last few months I got my sweetheart GCC Vesper a buddy (Temporarily dubbed 'Baby'). He's about 2.5-3 months old. Right now I am working with all of my birds to get them more tame, but I've been running into a big issue with Baby, in that he is very bitey with hands. Not just nip and let go, he clamps down and CHEWS! If he wants to bite, or doesn't get to bite my fingers, he will fluff up and throw a literal tantrum! I know GCC can be territorial, but even when he's outside of his cage he is biting. This morning, I went to clean their water, and he flew up to latch on to my hand!


Thankfully he has just began taking treats without biting, though sometimes he will still try, and sometimes I can get him to touch my finger for a treat, but otherwise he is a little monster. He's not aggressive in any other way, though. Sometimes he'll crawl over and sit on my arm, especially if Vesper is with me. But I have no idea how to break this behavior!

Currently I don't have anywhere to work with him except for in or on top of his cage, as we just moved into a very small building, and it's either the cage or the ceiling fan, and so I wonder if getting a tree would help? But I don't know if he'd bother if he had the choice of a tree or a much higher ceiling fan!

Please help!

 

[Dartman]

Pippen is the same way so she doesn't get any out time, but she has a huge flight cage all to herself with plenty of toys and seems happy enough. I do stop and talk to her a lot and scritch her through the bars when she's in a good mood, and she knows gentle means she's biting too hard and she usually backs off for a bit. The last time she snuck out when I was changing her water I put on a thick hood and put it over my hands and she hopped on and rode to her door with no drama so for her probably territorial and doesn't like hands trying to put her away.
When she first got here from being outside for a while she was super tired and a sweet heart but once she was rested up and feeling better she started getting aggressive and the little bugger can really bite when she wants to. I think she figured I needed to be punished for her being outside so long