If you have the option, I'd put the chicks together first. You may have to wait a little longer, too, but I introduced 20 five week old chicks to 4 year and a half old hens without a problem. The hens tried to peck them, but the chicks had a tipped dog crate they could get into but the hens couldn't. And 20 was too much for them. The little guys stuck together and would occasionally drive the hens away. They don't fight at all now.