Sadly we get very attached while they're babies and haven't reached sexual maturity. Once they do, you have to be prepared to make adjustments because they will no longer live in harmony.
Now, by that I mean, they can't be confined together. If you have enough space that they can separate and run away from each other, they are usually alright to roam together. But when you confine them to a coop and run together, they will fight, and mate, and injure each other.
I have a mixed flock of chickens, ducks, and geese. They roam the yard fairly peacefully together, but each species has their own safe space housing.