It's entirely possible to keep two conures together but it's not something that you should ever expect or depend on happening. If you add a second conure to the mix, expect it to live its life in a separate cage and anything beyond that is a bonus. Even then things can change between them and they may no longer get along. Someone posted here very recently about their sun and gcc not getting along at all anymore.
I had a blue crown conure that tolerated most other conures (but not 'tiels or lovebirds) outside of the cage. I had two gcc's that didn't like each other at all and then I lost one. I then got a black-capped conure and he and the remaining gcc got along very well right from the beginning and have been caged together for nearly 12 years.