How can I have my four bridesmaids in ivory dresses without them all looking like brides?

I am having four adult bridesmaids for our wedding next year, and have begun to think about dresses. I would love them all in ivory, or a sandy colour to match the men’s suits. My dilemma is that they would all prefer long dresses, but I am worried that if they wear long ivory dresses, they may all be too similar to myself!  The girls vary from a 5″1 size 20 to a 5″10 size 10 so it’s going to be tricky getting them all looking remotely uniform!