I would try again, but put the young ones in after dark, so that they can sleep together and wake up together. It also helps to have lots of fun foods scattered about: cabbage, melons, apples, treats and the like so that it keeps the hens busy. Add some cardboard boxes or other hiding spots so that the little ones can get away from the hens in the run. This also helps distract the hens by adding strange "territory" to their normal boring run.
If you lock them in the coop at night, be sure to get up really early before they wake up to open the coop door. It might be hard on the little ones if they are trapped in a small area when the hens see them for the first time. You also might find it hard to get the young ones to roost, but they will figure out that by in time on their own. If you have the room in your coop and run you can section off a small area for the young ones to stay in until the hens are more used to them.
Borrow, buy or make a small "jail" pen/ kennel inside you're run or coop for the mean bully hens and put them in "time out". But, there will always be pecking
just as long as they don't draw blood. It could take days until they figure out a pecking order, so be prepared. The pecked one will scream and complain, but it may not be as bad as you think. Wouldn't you yell back if a bully "pecked" you on the head?
Good luck