Can you tell me what "hatchery" means? I'm new...

I bought my chicks at Big R in Warsaw last month...
How old are they? If I have 6 chicks now - 2 buff orpingtons, 2 RIR, and 2 black australorps who are about 6 weeks old, can I introduce 2 or 3 EE's? Or do I keep them separate in a brooder like I did with these when I bought them until they are bigger? I wanted to have 6 hens and I was told there was a 90% chance they were pullets when I bought them but I am pretty convinced that 2 of them are roos so they will have to go... I currently have my girlies in a shed which I converted into a coop... I was thinking if I had to keep these new ones separate, maybe I could section off part of the coop so my others wouldn't mess with them and then when they all get the same size I would try to introduce them to each other? How do you guys go about adding chicks with your current flock?
Are your chicks pullets?
Sorry for all the questions! If yours are females and you think I could buy a couple I would absolutely love to, you aren't far from me at all...