How old are they? Does he/she hurt you when he pecks you? I think that you should just keep working with them. I read here that they can kind of go through a "terrible teen" time when they are adolesent chicks. Try to hold all of them for at least 2-3 minutes a day even if they don't like it. Announce your presence before you get near them by whistling or talking gently. I usually say "Hi girrrrrrls" so I don't alarm them by sneaking up on them. Slowly place both hands down close to them (some will come willingly, others you may have to catch) and put one hand under the breast and one hand on top of the back and over the wings so they can't fight. Their legs should hang freely. Bring her up to your tummy or your chest and talk to her while stroking her back, head, neck and wings. Mine all eventually came around after a week or so of being handled. Hope that works for you and good luck!
P.S. I don't know how to sex chicks and I don't have any roosters.....sorry!
Mine went through a phase where they didn't want to be picked up and held. Now they are older and don't mind. I just kept sitting with them and had some treats handy. I would give them a treat with one hand and pet them with the other. After awhile they didn't seem to mind the petting and then I started picking them up.