Neutering both males should definitely be a priority BEFORE any more attempts at introductions.
If you think one of the females may already be carrying joeys, I would leave her with King and keep the two of them separated from the others until the joeys are at least 8 weeks OOP.
I would introduce the other female (hopefully she is not also carrying joeys) to Flash to be his cage mate AFTER HE HAS BEEN NEUTERED.
You would have two cages to maintain for a while but if you think there are already joeys on the way, introductions could be very stressful for the mom and you risk the loss of the joeys by doing introductions now.
Keep in mind that any male joeys will also need to be neutered before they are 4 months OOP to prevent inbreeding with their mother or sister.