Depends what you mean when you say “attack” is it just pecking? Or is it other stuff (example: feather pulling, pecking till the point of blood, pulling skin and causing scabs)? I would recommend starting out by adding more then one water and food source, and if you manually feed them (no feeder or anything) then I would put the feed in piles, one per chicken. I hope this helps
That isn't mean, that is normal.
Teens don't lay so to mature hens they're not much more than food theives.
When they start laying the adults will work them into the group.