Hello and welcome to BYC! Glad you joined.
After your 30 day quarantine, the smaller girls should be put in a section of the run/coop that is partitioned from the rest so the original flock can see them but not touch them. After three days of this, I would allow the small girls out to explore the run with the original flock secured in the coop. After about 1 hour, let the large girls out and observe.
If you free range, let the small girls out first for about an hour then let the large girls out. This is the ideal way as they will watch each other but stay in two sub-flocks.
It takes a very long time before the two sub-flock will fully itegrate.
Good luck.