Jen wants to be a nurse. Her father was a doctor, and so these two combined gave her the medical knowledge necessary to deal with some unfortunate incident which befell them.
I'm not sure what York's ambition is, it wasn't necessary to the story, but he does have a dog. His dog is Canis, and Canis is very attached to his young master.
Jen was a dream character, she was in the dream about the fight on the bridge. That's where she got her name. York got his name because of Ian and Kansas. I was going to have a bunch of characters with state names, but in the end there were only three: Indiana (Ian), York, and Kansas.
York and Jen have a smaller role in the story than I at first thought, but they do have a role and they play it well.