Integrating Newbies into a Smaller Coop

We have a small yard and therefore have a smallish coop for our little flock. It's a basic coop/pen contained in one piece that you buy in the farm supply stores so it's quite small, which is ok because we only have a total of 3 pullets right now, with no plans to get more. My question is this: we have 1 pullet who we've had since she was a day-old chick (she's about 5 months old if that matters) and we just had to get rid of her little companion because it turned out to be a rooster. We just got 2 new pullets who are about the same age and came together from another flock. I want to integrate them as smoothly as possible, but I'm realizing it's much more difficult than I thought because of the small coop size. What do you all recommend? Right now we have the 2 new pullets in a dog crate up next to the coop so they can "chat" and get to know each other. It has a roosting pole for them and shelter from the elements (and of course a feeder and waterer) but I'm afraid they may get a bit cramped. How long should I keep them separate? Any suggestions, tips, or tricks are helpful! Thank you!