Introductions should be made somewhere neutral like the bath tub, to lessen any territorial issues. Do not try to do in one of the cages that almost promotes a fight to happen.
Scent swapping prior to introductions as mentioned will help.
Have a new or freshly washed bonding bag on hand. And a piece of fleece to protect your hands.
Put one bonding bag the gliders are in at one end of the tub and the other bonding bag with glider in at the opposite end of the tub, then put some treats in the middle. When the gliders come out of the bonding bags remove them from the tub and put the clean one in.
If they do end up balling up make sure your hand is protected with fleece and separate them as quick as possible. You can give them a minute and try again or call it a day and try it another time.
If they don't fight and all end up going in the clean pouch it's about a done deal!
At that point make sure what ever cage you intend to house them in as 1 colony is thoroughly cleaned, fresh fleece set, clean all the toys etc... to make the cage smell as neutral as possible before putting the gliders in the pouch in the cage.
Then just hang the pouch and let them wake up together in the cage... Keep an eye and ear on them for the first few days to make sure they don't ball up and fight.