I wouldn't even keep one bantam breed in that space. Imagine if you had to live in a very small...say 10x12 efficiency apartment for your entire life without being able to get beyond it. How content or healthy would you be? Now, share that space with 6 adult people. How would the quality of your life be then?
Think BIG when thinking of space for birds, for they walk almost continually throughout the day, pausing now and again to dust, preen or rest...but mostly they are walking and looking for food as is their instinct. These are not parakeets, these are mostly ground dwelling fowl and need ground on which to dwell...and lots of it.