What size coop to successfully integrate flocks

[Dirtbowls]

This is our current setup.

Thanks for the advice everyone. After talking it over with the wife we've decided to pass on the offered flock. We're going to build a new coop that will hold roughly 25 birds and then worry about adding in.

The flock did come with feeders, feed, use of coop until April, but the wife is concerned with adding disease to our current flock