What you are describing is very normal. Size has practically nothing to do with which chicken dominates another, bantams often dominate full-sized chickens. The personality of the individual chickens is what is important.
But you have something else working. Mature chickens always outrank immature chickens in the pecking order until they mature enough to be willing to stand up to the mature chickens. Until your pullets mature they will be afraid of the adults and will avoid them. Rightly so, the mature ones are likely to peck any immature chicken that invades its private space. Occasionally a mature hen will seek out an immature chicken to attack but once basic integration is out of the way that behavior normally stops. Still, until they mature the younger ones will avoid the older ones. Normally my pullets mature enough to join the flock around the time they start to lay. On rare occasions that might be a few days before they start to lay but usually it’s a few weeks after they start. I’ll say it again, it has nothing to do with size, with yours it’s maturity.
I agree, do not force them. Allow them to work it out. Provide separate feeding and water stations so the young do not have to challenge the older ones to eat and drink. Since yours free range I assume your older ones spend most of the time out of the coop during the day when they are not laying eggs. The young ones should be coming down to eat and drink during the day when the older ones are outside. The way I read your post you have food and water in the coop.
When I integrate younger chickens I usually find them on the roost in the morning when I go to let them out. They are avoiding the older chickens that are on the coop floor.
Chickens don’t like change. Those two have not yet adjusted to their new home. It’s not that unusual when I open a pop door for the first time with new chicks for them to take a while to venture outside the coop. Sometimes they do it in 15 minutes, but I’ve had some that take three days. That’s without any older chickens around for them to be afraid of. It shouldn’t be that long before yours discover the great outdoors and start going outside. When they do that they still will not join the older hens. They will stay away from them to avoid them.
There is the possibility that you do have a chicken, probably a hen, that goes out of her way to attack the pullets when she sees them on the ground. If that is the case the pullets may take longer to come down and go outside. They are safe up on the roost. I sometimes see that behavior when I have pullets and rambunctious cockerels in the flock. The pullets spend a lot of time during the day on the roosts to avoid the cockerels. But eventually they work it out. But if you can identify one specific hen that is attacking the pullets when they go to the ground, isolate that hen. Lock her up so she cannot attack the pullets. That should help them get outside. It’s quite possible that after a week of isolation that hen will go through an attitude adjustment and quit attacking them.
As I said, this is all pretty normal, I often see things like this with my flock. But sometimes, and this year is one of those years, the immature chicks raised with the flock by broody hens do not avoid the adults once they are weaned. The adults do not attack them when they invade their personal space so they intermingle a lot, even as juveniles. Each chicken is an individual, each flock has its own dynamics. It can be fascinating to see how much my flocks differ year to year with the addition or subtraction of a few birds. Just be patient and let them work it out. They should be outside foraging before too long.
Good luck!
