welcome to pet talk. Cats sooner or later will settle their differences. In the case of Chrissie, I would have you do as I do with my Fern. She has always been shy and afraid of the others. I try to prevent the others from picking on her as much as possible, but I have noticed that even though she really hates it when they bother her, it has somehow brought her out of her shell MORE than when they did not bother her. (if that made sense). your newest may well be trying for top spot, and he may or may not get it. But they will figure it out with time and patience. Don't be afraid to use a squirt bottle to curb any rough stuff. Good luck