Right off the bat I would say tht it sounds like she needs to be on a 4 hour EASY for her age. Even newborns don't *really* need to eat 2hours a day, let alone a 4 month old.
I would also say that if she is feeding that much, it's possible that she wants to suck. Does she take a pacifier?
As for Sera, I suggest a special basket of toys that come out only when you have to manage Rose. Is that possible? Get her some toys/coloring books/regular books/dolls/dress up whatever, that she has helped select that you KNOW she likes, and pull it out when you are helping Rose.
Let me know what you think,
Lu