Choosing one gal to show how great a bond can be ,That is an awesome idea. So many great ideas! You are doing all the right things, The 3 T's Time-- Treats and Temperament.You might select one hen to single out and separate to work with along and maybe you could win her over by herself and focus on getting her broken and then let the others see that she trusts you and then let them follow the leader.
I have a new gal(Maizey) that is also skittish, she was raised in a coop and never held either. She chooses to roost in the patio instead of the coop. Before I put her in the coop, I take some time to hold and pet her, she's slowly coming around.