I don't think it is how much they sound, but the image you see and what you want them to do. Ashley, my girl, I created under a different scenario 12 years ago. She is very strong. Everything I tried to put her in didn't work until this story.
At the risk of sounding like I have totally lost my mind, yes you can have conversations with them. My husband, when he was still alive, use to give me really strange looks when I would be talking to Ashley at the table trying to get a story going. She would be arguing back as to why not. Then I came up with the present scenario and it wasn't until I had to completely redo her bio it was a go. Now I am just afraid of the narrator not coming through (me).
I guess what I am trying to say is just let the idea hit and you will know.
Kristina