I've never had problems with mixing cot's. As long as there's plenty of room.
Are they all hens?
Yes, they are all hens. They're going to have 6 square feet per bird, a 50 gallon rubbermade full of white sand, and a smaller coop filled with straw and leaves for hiding, so their shouldn't be too much competition. I'm thinking if I give them extra feed for a couple weeks, that should decrease competition for food.