If they are balling up, you need to separate them because one glider could injure the other. I don't know if swatting at each other is good sign either, but as long as you are nearby and ready to separate in case they ball up in a fight, I guess it should be fine. And I would agree in not putting together in a cage as of yet, wait until they are no signs of aggression (i.e. the swatting).
The psst noise is usually a glider telling another to back off, is not done with aggressively, but among gliders that are just being introduced it could be the first signs that they may start fighting. Just be very watchful. And good luck!