The males will naturally be a bit larger but you would not want to put a joey half his size in with him.
My joeys were pretty close to their Mom's size at around 6 months old, she is on the petite side (Daddy is my chubby guy). The twin joeys just turned a year OOP on July 31st and the boy is noticeably bigger than the girl.
The girl and her Momma look so much a like I can barely tell them apart now. I can tell by their personalities who is who because the little girl is very out going and friendly and the Momma is very shy and reserved.
What ever gliders you decide to get you will want to vet check them and have fecals done and then do a second fecal test in 30 days. Then you would start swapping sleeping pouches and toys, moving there cages together about a foot apart so they can smell and see and talk to each other without being able to grab the others thru the cage. That usually goes for about 1-2 weeks.
Then you would clean the cage you want them to share very well, wash all items in it or use brand new stuff and introduce them to each other in the bathtub (in a glider proofed bathroom)during the day when they are sleepy.
When they crawl in the clean sleeping pouch and sleep together all day, they should be fine. If any of them were to "Ball up" and attack each other...they need to be separated right away(check for any wounds from bites) and start over with the scent swapping.
There is a link on introducing gliders in the Gliderpedia tab too.