Also, thanks Tiaris for the great advice. I actually have a situation where all my hens are siblings, but it's largely a coincidence. Cock birds seem to be so much easier (and cheaper) to get a hold of around here, so I've always just kept my own hens for future breeding and sourced cocks from elsewhere.
Noted, however I care more about having an attractive display of different birds than optimum breeding results. I'm breeding well above replacement rate, and there's much less work involved when they'll all in one big aviary. (Well, two actually, I maintain a second mixed finch colony for young/old/spare/for sale birds)I find single prs per aviaries gives you far better results then colony breeding if possible.