I think you can as long as they are raised together. If you bought them all as chicks and they grew up at the same time I don't see a problem unless you keep roosters. Chickens will attack and kill any new chicks or chickens if they aren't given a few days to a week of introduction time. I usually put new chicks in a box with a wire lid on it into the chicken coop so the older chickens will get used to them before releasing them into the group.
I had someone dump a chicken off at my house. I thought it was one of mine that had gotten out. I put it in with mine and before I realized it was a "chicken dumping" they had killed it.
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France