Chickens have a pecking order. The hens won't usually fight to the death like game cocks but they will fight. Sometimes one will puff up and the other will yield other times they will fight fiercely. You will just have to watch them when you put them together. I don't know how your pens are set up but it is also a good idea to make sure that the looser has a place to get away. Roost are a good idea. If you don't have a good escape, watch that the dominant hen/hens don't drive the weakest into a corner and kill her. Also, make sure that they all get plenty of water and feed. Sometimes, Aggressive birds won't let the others eat or drink. I hope that helps some. I have had birds for years but I am new to this site. I am sure that there are other good suggestions on the site. Just learning to get around myself.