Well I said you might have to repeatedly try letting them out, though only two makes for easy targets, perhaps wait a couple of weeks then try again, I would make a small pen inside the pen with some chicken wire or hardware cloth, so they can be with the others but not get to them, you are going to have a problem because the older are not old enough to think of the young ones as chick, they see them as competition, it's going to take a while, most likely until the older ones forget they don't know the younger ones, and probably until they begin to lay, it's a situation that will take a while, don't rush it, they have a couple of weeks before I would integrate them permanently, 8 weeks is a good age, eventually everyone will mostly get along.