Hi,
A 4x2x2 viv is recomended for 1 adult beardie and the general rule is you would add 2 square ft per additional animal in viv. I Don't really recommend keeping more than one dragon per enclosure as it can lead to a bunch of problems. Like dominace issues, compition for food which can lead to injury's or possibly death. Also if one of your dragons becomes sick it could pass it along to your other dragons before you even know it. Although some have sucessfully kept multiple females in one enclosure I wouldn't house a male and female together as the male will tend to overbreed the female affecting her health and possibly death. I originally was like you and wanted to house 2 females together in a 7x2x2 enclosure but one of my females was not liking this idea and would not get along with my other females(good thing I had built the cage with a devider for just this reason). If you wanted to setup a breeding colony I would get a bigger enclosure and see about housing 2 females(be prepaired with another enclosure if they don't get along). Then during breeding introduce the male to the females for a day or 2 at a time and see how it goes.
Hope this helps..)