How old are these chicks? If they are under about 2 weeks old, there is no problem. Just bring the new ones home, pop them in the brooder, and they should be fine.Oh and also wonder if adding new chicks to the clutch would cause problems... if we do choose to get 1 or 2 more, does it matter the spunk or other characteristics of the new ones for a better transition?
If your chickens live in that space all the time, and never come out, I would consider it good for about 4 chickens (staying in the 4x4 area in bad weather, using the bigger area as a run in good weather.)sorry I had to go measure. So it is 11.5x4 feet enclosed and covered long run area plus a 4x4 area (that can be enclosed with bad weather) off the ground not including 3 laying boxes.
Your climate will have a big effect on whether they need to spend much time in that 4x4 more sheltered space.
And if you have another big run attached to that, where they can spend most of their days, that can also make a big difference in how many chickens live comfortably in that size pen.