I recently had the pleasure of making two sibling sets of layer dresses. One for my good friend Anne and her two daughters. They are about 18 months apart in age, but pretty much the same size. We picked out some fun safari-type fabrics and coordinated the dresses without making them identical. You can't tell from the lighting of the photos, but the fabrics are the same :) The fabric for these was Fabric Central Exotic Bundle 2 plus an extra fat quarter of the yellow fabric purchased from JoAnn's.
The second set was for a friend of Anne's two daughters who are several years apart. This time we went with fabrics that were "pink and girly" by the client's request and the dresses were made in different sizes. The fabric for these was Bloom and Grow by Riley Blake in the pink and cayenne colorway (purchased at Karamat on Etsy - great service!)
It was so fun to take a design I made for my daughter and make it for others too!