It’s also two versus, I count seven? I have had good luck integrating chicks when they outnumber their elders. Each baby only garners so much of the negative attention from the older birds. They also have one another to socialize with and don’t have to keep approaching the older birds for company. I’d continue with supervised integration. One day, probably very soon, you’ll just feel comfortable leaving them together. You’ll see the older chicks ignore opportunities to pick on the smaller ones, they’ll wind up eating alongside one another, perching together, fleeing from “danger” together, and it will click. Younger is definitely easier. I just did 16 chicks at two weeks with 12 chicks a month older. It only took a week of contact in separate quarters and a few days of supervised time, and I was probably overly cautious.