i'm just curious. i only have one green cheek but when i'm at my local bird store and around another bird owner he tends to get a little spooked by the other bird(s)
Presently have six Greenwing Macaw (17 yo), Red Fronted Macaw (12 yo), Red Lored Amazon (17 y.o.), Lilac Crowned Amazon (about 43 y.o.) and a Congo African Grey (11 y.o.)
Panama Amazon (1 Y.O.)
Depends on the bird, and how well he is socialized.
At one time, I had three conures inside my shirt, an amazon on one shoulder, a large macaw on the other, another amazon on one hand, and a CAG on the other. Mine were raised as a flock, and "big bird" (i.e. me!) tends to gets upset if they argue. So they didn't argue. They were raised that way.
Only birds might not necessarily want company, especially pair bond birds, and might try and drive the other bird out of the nest. Or they could bond with the other bird. Or some combination of all of the above.