You will need a second cage.
Before introducing the birds in their seperate cages, you will need to run a full 30-60 day quarantine. THIS IS SUPER IMPORTANT Many birds can carry an illness and not be affected by it until they are stressed, new situations, new homes and meeting other birds can bring out illness. Trust me, vet bills for one are MUCH cheaper than for two. There is no discount for bringing in two birds at once.
Second, what will you do if they don't get along. Not all birds, even of the same species can be friends. In fact, they can kill each other if they don't get along.
Third, what will you do if you end up with a male and female. Are you prepared to prevent breeding? If they do manage to breed, are you able and willing to provide for up to 6 more birds?
All that being said, having multiple birds is wonderful. They do entertain each other, but their bond with you is not nearly as strong as a single bird household. Food goes much quicker, cages must be MUCH bigger, and you need to always have a second cage ready in case they fight or one is ill.
Please go to my
site and read the article about protecting your birds through quarantine. It will explain all that you need to do to keep your current bird healthy and safe.