It's normally not a good idea to immediately add new birds to your flock. Chickens can transmit disease from another flock to your existing flock. If you have the space, I would keep them separate for a week or so and observe them for any symptoms of illness. By adding them to your flock, there will be a readjustment of the pecking order and your new hens, especially if they're smaller, will be picked on. Normally, the pecking order sorts itself out in a few days but you need to keep an eye on them. Sometimes, the older hens will peck them unmercifully and the new ones may have to be separated for their own health.
You're fortunate to create a 'target rich' environment by introducing more than one new bird as the flock will be prevented from concentrating their pecking on one bird. You may want to set a separate feeder and waterer aside in your chicken run for the new girls as the old ones may prevent them from eating and drinking from the old facilities for a while.
Bottom line, you can introduce new birds but watch for disease and keep an eye on them closely for the first week.