Need help with integrating chickens!

Hi! I would really really appreciate everyone’s help and advice.

We’ve had chickens for 5/6 years now. We started with a flock of 6 and are down to our last one. Our second to last one died a week ago. I got 4 chicks in late fall and was raising them in the garage until we could put them out with the chickens. I had a lot of anxiety about joining the 2 groups but once we were down to one I knew I needed to do it. We had a blizzard a week ago so I brought the last one into the garage to keep her safe. She was in a pen right next to the younger chickens pen so I was hoping this would ease the transition of them being in the coop together since they’ve seen each other for a week. We put our original back out in her coop 2 days ago and put 2 of the younger chickens out on the roost below her roost she was on at night. I heard that was the way to do it…put the new chickens on the roost at night. The next day our older chicken was attacking the 2 younger ones. They’re afraid of her now. Last night we put the last 2 out there and now I just saw on our camera in the coop her going after them horribly. I’m not sure what to do here. I know they’ll be some pecking to establish a pecking order but it seems excessive. Do I bring the older one back into the garage for a few days until the younger ones are comfortable and used to the coop? I’ve never introduced chickens to each other and it just makes me worried and sad for the younger ones. I don’t want them to get hurt. Any advice would be so appreciated! And sorry for the long rambling!