imo mixing 'not mature' birds theres usually very little problems but of course you cant mix tiny fuzzballs with 4 week olds, use your head .. also 'lots' of space usually eliminates serious problems, but pretty much mature birds simply will not accept immature birds in their space, again, there needs to be enough space they can occupy different areas if you want to put say 5week olds in with old crusty mamas .. 'no' they wont 'get used' to each other past the point of 'likely wont kill them', the older ones will always kick their behind .. as long as they have enough room to keep good distance, like 8' theres usually not much problems .. confine them yeah, theres gonna be carnage .. once everybody reaches sexual maturity, things calm down into a normal pecking order ..