That is tough to be in that spot you're in. I think it best for you to take a few things into consideration:
1. Can you take on another glider, even if it may mean managing two cages permanently, if they do not get along?
Or
2. Can you assist in finding this lone glider a new home, a better home than in currently, even if it means you take him in temporarily to improve his life quality and rehome him yourself?
I don't know too much about young gliders to give advice or thoughts on whether there would be an issue with the two males and one female, but a third thing to consider is the fact that they're still fairly young, and that may be something going for you in this situation. I'd like to let someone with more experience offer more on this prospective.
Please update us on this situation. I do hope this glider finds his way into a good home one way or another.