Hello all, this is my first post on glider gossip, though I have been here many times when in need of info for my babies.
I have 2 gliders {neutered brothers, 2 y/olds} that my partner and I have taken care of since they were 8 months old. We love them to death, and have made sure they are in good health. Yesterday we saw a post on craigslist of a single neglected glider that needed rehoming. She was 3 years old and alone, and we believed that we could give her a better life and playmates. The person who gave us the glider also offered the cage on the listing, so we knew that if it didn't work out between our gliders, we would be able to keep the cages close, and look into other options. (We know the procedure of carefully introducing gliders to one another, we had contingencies in place for that). HOWEVER, we did not expect what happened when we finally got her, and unloaded her into a cage.

-Her fur is dark.
-her eyes seem a bit sunken
-she at first seemed to drag her hind quarters but started walking normally after a bit.
-When she first got into the new environment, a drop of what looked like water came out of her nose and mouth area.
(Im assuming thats what is referred to as hyper salivating.)
-Her tail is tiny, fur missing in places and the tip is black from what I assume is a scab.

Self mutilation for sure. She kept pacing the bottom of the cage as her owner had kept her in a rat cage instead of a sugar glider cage. As the night progressed I gave her some yogurt drops to just calm her. We left her alone to climb and explore, and find the pouch. Eventually we put some food in and she chowed down. Throughout the night she seemed to get more energetic and act like a normal-ish glider.

We didn't know the details of the negligence she lived in when we first picked up her up, other than she didn't have a cage mate and was lonely. After picking her up and seeing the horrid condition she was in, however, the previous owner admitted to the following

-she was 5 years old, unspayed
-her mate died
-she had a baby, who also died because a dog got a hold of her
-she lived in a house with smokers
-she has a hard time climbing because she's used to being on the ground of her (rat) cage
-she lived in fear of 3 cats that lived in the same residence that would crowd her cage

In summary, this glider has been severely abused to say the least, and I worry introducing her to my boys because of her fragile state, and I am even more afraid they could kill her because they think she's sick. I also don't want to leave her alone in her cage because she is lonely. What should I do? Should I risk introducing them? What kind of tests should I ask the vet for before putting them together? Does anyone have experience with "rescued" gliders?

I am in over my head, but I couldn't let her stay in that environment.

I think you should give him nutrition first, feed him gently beforehand like a rather runny fruit juice but don't add sugar, let him rest, give him a room that is not too bright and make sure the room temperature is not hot. may be useful