FOOD! My chickens love any treats - ie mealworms, stale bread, cucumbers, squash, kitchen peelings, etc.
Most of my spoiled hens are cuddly since they're used to human interaction, but there are always some that simply don't want to be held. Those learn to come when called & eventually take treats from my hand - but they'll never enjoy being touched.
As far as the hen flock intro, I first do a quarantine period. After that, I do a temp set up nearby- the "look but don't touch" approach. After they get used to seeing each other ( maybe 3-7 days ), I slip the newbies in at dark when all are asleep. They can't fight in the dark b/c they can't see. By morning, they'll be a few pecks, but they don't all out fight b/c they already spent the night together. This has worked well for me.