One of the biggest issues I've had with introductions in the beginning, was over thinking it and being nervous.
I recently introduced a 14 week oop petite joey ( under 70 gramas at the time) that was living with her parents one of them being an intact male. To 3 mature gliders, 2 of them very large in comparison of the joey, almost 200 gram female and a 164 gram neutered male, and the other a very tiny mature glider 70 grams a tiny bit bigger than the joey, with minimal scent swapping.
I let the joey and parents pouch get stinky and grungy, same with the other trios pouch stinky n grungy.
Gave the joey's pouch to the other trio for one night to sleep in.
Took their pouch and put the joey in it the next day and rubbed her allllllll over with the stinky grungy pouch for about an hour. Rubbed her with the pouch while she was in the pouch to make sure the other trio's stink was on her as much as possible.
Took both pouches of gliders and put them on landing of my stairs which is a smaller space than a bathtub, pouches facing each other and put treats in the middle.
My biggest female glider went in the joeys pouch and loved on her, then my male went in and was loved on, then little Amy went in and decided the joey was hers.
This introduction took less than 5 minutes, 3 weeks later then haven't had any issues at all. I also didn't thoroughly clean the trios cage, or make it neutral smelling in any way, after the intro I kept them all in the same pouch in my lap until about 9 pm then just put them in the trios cage. I did add a 2nd plate of food and have continued to use two plates for food because my plates are to small for portions of 4 on one plate.
My point is, size is not always an issue, Knowing your gliders IS. Scent swapping for a long time isn't always necessary either, I paired the joey up with these 3 because they are the most accepting of new cage mates, I did ONE night of scent swapping for the trio and ONE hour for the joey.
The joey has already grown enough that she is now a little bigger than Amy who is now back to being the smallest in the cage. The joey wasn't intimated by any of the other gliders sizes and they are not only bigger than her but also bigger than her parents were as well.
The biggest thing I can tell you is once you make a decision to introduce, be CONFIDENT in that decision, be calm during introductions but still be prepared to intervene if necessary. The more nervous about it that you are, the more nerved up the gliders will be.
Have a piece of fleece near you to protect your hand if you need to separate them. Trim their nails before introductions. Have a bottle of vetericyn VF on hand in case they do ball up and one or both gets scratched.
I've done a lot of introductions, using a few different methods. Some were successful long term, some were not. Knowing your gliders and being calm and confident are key in any introduction.
Top right is the joey bottom right is Amy, top left is Simon and bottom Left is my porkchop Nicky.