Introducing Pairs

I've successfully introduced single gliders before, and they've ended up happy cage mates. That process was actually relatively easy. We're getting a new pair today (fixed boy & girl) and I wanted to see if anyone had suggestions on how to introduce them to our current pair (females). The new pair is apparently 3 years old and have been, from my understanding, together the entire time. Our current pair have been together since December when we got a joey to replace a cage mate that had passed. Anyway, any suggestions would be appreciated; if more info is needed, ask and I'll do my best to answer.

TL;DR - Need suggestions on how to introduce a new fixed boy and girl pair to our current 2 females. New pair is 3 yrs old, current pair has one that is at least 3 and one that is less than a year. Current pair have been cage mates since December.

Edit: They've been dropped off to us and they are FAT! I'm not so keen on the diet they've been feeding them. We've always used BML to great success, and these new ones are on the NutriGlider diet of which I am not so familiar. Should I mix the NutraGlider stuff with some BML and gradually wean them onto the BML to make the transition easier or just offer solely BML right off the bat?