The way it's looking now if Joe moves to DB or plays both sides a little bit, with his athleticism he could "escape" the thought of being the next Reggie Bush, a.k.a being outgained a full yard per carry by Pierre Thomas.
Joe is a solid player and I'm sure his brother will be pretty solid as well, but USC is way bigger than these two guys and if Joe's not happy with his situation then I doubt Jonathan goes there.