So I decided to do something rather risky today...
Georgie and the cockatiels have seen each other enough times to recognize each other. In addition, Georgie is healthy and so are the tiels. I sometimes don't have the time to work with Georgie alone and let the tiels have out of cage time in the same day, and Georgie has learned faster by watching them than he ever has with me having one-on-one time with him.
So, I decided to try moving Georgie in with the tiels. The cage itself looks to be big enough to fit 4 cockatiels and maybe five budgies (or at least five of the smaller parakeets). I'll be keeping a close eye on them for about a week or two. If they end up not getting along, I'll put Georgie back in his little cage and possibly keep him in the same room as them so he'd at least be around other birds and not feel lonely when I'm away in college. He would also be around me more often and I'd be able to interact with him while I interact with the cockatiels.
So far they seem to be doing okay today. I put a piece of millet spray near where Georgie was sitting, and Lucy started eating from it. Then Alex tried to get to it, but as soon as Georgie started going towards the millet, they both got out of the way quickly.

Then Georgie started eating the millet (FINALLY he learns that the millet is food), and both Lucy and Alex were trying to figure out how to sneak some bites. The piece itself was a little too small to share so I decided to put a bigger piece in there and put it in the middle of the ladder so there was enough room for each of them to eat from it while staying a safe distance from each other. Lucy was the first one willing to eat with Georgie.
I left the room for a bit to see if they'd behave while I was gone. From the sound of it it seemed peaceful. Then there was some big noise; I think someone tipped the foodbowl on the bottom (I put Georgie's food bowl on the bottom because I can't hook it to the walls of the cage because of the design of the cup), but I go in there, and Alex and Georgie were both near the millet, so I think they were sharing the millet at that time too.
The only problems they ran into was between Georgie and Alex. At some point Alex was pecking at Georgie. Georgie didn't notice at first since Alex was trying to do it from a distance, but when Alex did manage to actually touch him, Georgie retaliated. Now he doesn't let Alex get close to him.
Granted, this was exactly what Alex did when she and Lucy started sharing a cage. Alex would peck at Lucy to move, but Lucy would be too stubborn to move and would peck back, and they'd have a disagreement. It would only last a few seconds though and then they would get over it. Their disagreements don't happen as often now, so I hope this ends up being the case with Georgie. If it escalates, I'll have to separate them.
They had a night fright when I was going to get something in the dark, but after turning on the lights, sitting there next to the cage, humming the cockatiels' favorite tune and just generally telling them it's okay, they went back to their respective perches.
Here's hoping this goes well.