If the cockerels have grown up together and there are enough girls to go around (you may need a few more) there's a good chance they'll co-exist happily.
OEGB are my favourite breed and ours live and free range with our bigger birds (who have always had bantams as part of the flock). It's the cutest thing seeing them fly to you when they see you coming and having them crowd around your feet. They are extremely active and busy birds, jumping up into the trees to perch and crow, scratching for bugs, running flat out and play fighting when they are young. I have one raising some chicks for me at the moment and another who is on eggs. They are excellent mothers.
I personally don't think that indoor aviary has sufficient floor space for such active bantams. It also does not look that easy to clean (chickens, even little ones, make a lot of mess). The wire netting would be a potential bumblefoot hazard as it would collect poop (being small mesh designed for small bird poop, not large chicken droppings) which would then harden, leaving sharp edges. It happens often with quail when people keep them on mesh that's too small and/or is not kept scrupulously clean.
They would have a more interesting life outside where they have a flock to interact with, a dust bath (which would be too messy to provide indoors), space to run and jump, and overall more to do than being in a small cage. They are also very fast and nimble, so if they don't want to be caught (because they know you're taking them back inside after they've had the freedom of free ranging) you've got no hope. They are smart chickens.
I adore ours and it is tempting to keep them inside because they are the sweetest things and they really are pets if handled a lot, but when you see them enjoying the outdoors you'll know that's where they should be.
If you can't let them free range all the time I would suggest a big, tall, covered run so that you can easily go in and sit with them.
We have plenty of outdoor space, coops, and runs, and they can free range, but I read it should be supervised?!? We are in a 4 season area so the will not free range in the freezing times.
