By crying, do you mean crabbing? Is the glider making a noise that sounds something like a duck crossed with an electric pencil sharpener? (Best way I can describe it). If so, that's called crabbing. Unless you have a real reason to believe that the glider is in some way injured, or has recently experienced some emotional trauma, then there is a good chance they are just crabbing because they don't really know you. Even if their friend is fine with you, that doesn't mean they are ready to accept you. Try backing off a little. Sleep with some fleece scraps, or wear some inside your clothes, then put them in their sleeping pouch. This will help them get used to your scent. Try sitting with them in the dark at night in a small, glider-proofed space. This will allow them to run around and explore, but also get to know you in a relaxed, organic way. Many people, including myself, like to use small tents to do this in. A bathroom will also work well. Treats are great ways to buy their affections (yogurt and meal worms are favorites here). Patience is really key with these guys.
And as others have said, you definitely can't potty train them. Once they start to really like you, they'll start saving up their pee for you, so they can mark you as their own.