I think that if they get along well enough to have play time together, they should be living together. Gliders really like to sleep in a huddle, rather than alone. If you have your male (and any possible male joey) neutered, you would have a stable, happy little family. In my opinion, that would be best for Kiwi. I had a lone male for three years (!) and since he's had buddies, he's a much happier little guy. Once introductions were successful, I could not have left him living alone, being with his friends only a few hours a day. It just wouldn't have been fair.
I'm just curious, why would you not want to neuter the little boy?