You're welcome. You can add as many as you like to the flock as long as they are approximately the same size as the ones you already have and you have the coop space to handle them so that they are not overcrowded. If you do add more to the flock, just be sure and do so slowly and carefully using the "look but don't touch" method. There's a good article at https://poultrykeeper.com/general-chickens/introducing-new-chickens/ explaining how to do it.
Thanks for the article. BUT... they keep multiplying.
I'm not certain why they are multiplying unless you have a rooster. If so, remove the rooster and they will stop multiplying. It's fine for you to have a flock of four (or even less) as long as they are all hens, but if you're keeping a rooster you need more hens as the recommended ratio of roosters to hens is 1 rooster for every 10 hens. As they mature and their hormones kick in, too many roosters (or too few hens) will become very hard physically on your hens, over-breeding them, biting and plucking the feathers from their necks and backs, battering them, and potentially, seriously injuring them. The only reason you really need a rooster is to fertilize eggs for hatching which is exactly what it sounds like you don't want to do. Of course if you only want to hatch a few chicks on occasion, you can always keep the rooster separated from the hens where they can see each other but not make contact and then let the rooster in with the hens for a very short amount of time--just enough to fertilize the eggs you want to hatch.Thanks for the article. BUT... they keep multiplying.