If you just pop them all into the coop yes, a fight will be on and it will be ugly. Can you fence off part of your run for the new birds? And at night try popping them in a dog crate inside the coop. The idea is to let everybody get used to seeing the new birds around for a while before they share space. Chickens can be really horrible to new birds and if they get it in their head to attack to the point of serious injury it makes it that much harder to accomplish integration. It will be easier since you'll be introducing several new birds and not just one but if you let them gradually get used to each other it will be even easier.