You have to let the birds decide if they like each other or not. You need to only put similar birds together, so that a more aggressive species doesn't attack a docile species.
First study the species you wish to have. Purchase separate cages for each bird. Allow the birds to play together in a neutral place, ready to rescue (and get bit) any bird that gets attacked.
Rather than continue this, I will point you to an article I wrote about how we got our two green cheeked conures to accept each other and eventually live together.
Please read our "Should I get another Green Cheek Conure" story on our Parrot Training page.