Sibling rivalry in the tween set
DD's nephews have moved in... They are little ones (preschoolers, toddler), and DD is fairly jealous already.
We try to make her a "grown up" as far as offering to let her "babysit" the older 2 outside (fenced yard), asking her to help us care/manage them. I'm also making a heck of an effort to take her somewhere by herself for a few hours for some one-on-one time.
So, suggestions on how to work through sibling rivalry with the tween set?
Sibling rivalry in the tween set
The problem in your situation is not traditional sibling rivalry, but someone who is not a sibling and disrupting her world. Please don't take this the wrong way, but having people constantly move in and out of your house is going to be really hard and disruptive on your daughter. It's only natural for her to be jealous. I wouldn't give her any more responsibility. She didn't pick this situation. They are not her siblings. Id let her have more space and make sure she's getting enough positive attention from you and alone time with you.
ETA: I have a tween (9.5) and a toddler (2), and he always getting into her stuff.