You don't say how old the pullets are and I don't know what your facilities look like. With only 5 total chickens that kind of implies the coop may be relatively small. That information might be helpful.
Today they free ranged all together, and besides a few pecking order squabbles, all went
So is today the first day they all free ranged together?
In the past, the pullets had been roosting in an enclosed part of the run. I’ve had to move them in there each night.
Knowing what it looked like could help but that sounds a little strange. If they are used to sleeping in that area they should want to go in there to sleep on their own. You should not have to move them in there. I'm not sure what is going on with that.
I figured since I left it open to all, the younger chickens would take the lead of the older ones.
Mine go where they are used to sleeping instead of following the adults. Nothing unusual here to me.
Any suggestions of how/ when to get them into the coop together as one big happy family? Preferably on their own?
What I do is let them free range together for a while so they really get used to each other. I don't try to move them into the same coop at night until they have proven they can get along during the day without any squabbles. They do not have to intermingle during the day, but no attacks or squabbles. I let them sleep in their normal place at night, not forcing the to try sleeping in an enclosed coop together for a while. With mine that's usually a few weeks but the way I'm set up that's not a problem. If you have to move them every night or the extra space to clean is a chore I can understand you wanting to get it over with.
My goal for integration is that no one gets hurt. That's it. No one gets hurt. That big happy family can and will come later. Until my pullets mature enough to join the pecking order they typically avoid the older hens day and night. If they don't they are likely to get pecked. That's why how much room you have in the coop is important and why things aren't usually to bad if they are free ranging. Lots of room when they free range.
my older hens need the space throughout the day to lay eggs and to eat
I understand that, I don't want to train my older hens to lay somewhere other than the nests. When I'm ready to move the chicks into the main coop I wait until dark and toss the chicks in. It's too dark for the older ones to attack them and I'm out there the next morning when they wake up to see how it is going. I don't bother trying to set them on the roosts or anything like that, if that is close to the adults they aren't going to try to sleep there anyway. I personally don't care where they sleep as long as it is not in my nests and is somewhere predator safe. They will figure out a place.
Sometimes I only have to do that once for them to put themselves to bed in the main coop, sometimes it takes a few consecutive nights to get the message. If that coop is so small thy can't find a safe place to sleep away from the adult hens this can get challenging.
Good luck!