my wife has done 4 introductions. 2 plus 2, 4 plus 2, 6 plus 2 and 2 plus 1.
with all of them she started with 2, then switched in another one so it was still 1 vs 1. then worked up to 3 or 4 all together, usually giving 1 vs 1 about 5 minutes in the bathtub. Small spats were allowed, but bigger spats we separated and tried again later or next day. 2 plus 2 was easy, 2 plus 1 was easy (they had some introductions from previous owner). 4 plus 2 was hardest, and 6 plus 2 went well.
usually our gliders were glad to have more friends, it was just they need that initial intro to go well and see that neither whats to fight, then they are happy to have more sleeping bodies in the pouch.