I'm so sorry you are having so many problems. Must be VERY frustrating. And.. frankly, would make me SUPER angry at them.
My question would be how old are your chickens?
About a month before mine started to lay they were HORRIBLE. Everyone picked on everyone else. We had just lost our roo, too, but hadn't had him long so don't know if that added to their irritation.
Got a new roo (he's a d'Anvers.. and they are all standard sized), and they started laying. No more pecking at all. And I do think my girls are bored.. they have a big covered run, but won't free range right now because of the snow. They seem to be ok, though. There was one girl who got chased a lot (although not pecked). After three months of her own personal h*ll I sprung her, and she's part of a new mini flock of bantams. But she seems to be the only one they had singled out (and actually they were finally leaving her alone.. but she still wasn't happy). Some birds just don't fit in, I think.
Another thing I've heard is hanging veggies or shiny objects to give them something to peck at.
Do you have food out all the time, or only at certain times? If you only feed at certain times, they have lots of time to get bored, too.
Hope that helps. Don't give up! Once the warmer weather gets here, they'll have lots of bugs and grass to munch on. I'm sure they'll do much better then.
Meghan