Sienna and Savannah Miller are two siblings that have definitely learned to share. The stylish sistersand former roommatesco-design a line that ranges from frothy dresses to lean and mean jeans. A recipe for rivalry? Not a chance. "Sienna's edgy and out there; I'm soft and romantic," Savannah told a U.K. newspaper. "I have an idea for a design and she adds the sex and flips it on its head. It's fun and it works."