Why did you ask the members of your WP to be in your wedding? What are you requiring of them on the day of/prior to?
I have 4 on my side - my brother, who is one of my very best friends, my two long-time best female friends, and my daughter. I asked my brother because he is the only member of my family that I am close to and one of my best friends - it means a lot to me to have him standing there supporting my choice. He may also end up walking with me. My two friends have been with me through all the hardest parts of my life and have always been there for me, and me for them. I couldn't imagine the day without them. And my daughter (who will be 10 at the time of the wedding) is one of the most important people in my life, just an all-around awesome person, and it's also important to her that she gets to be part of my wedding. She also adores her stb-stepdad.
I picked these people because they are the most important people in my life (other than my FI) and I love them.
They are choosing their own dresses (pref satin but I am flexible) and they can pick their own shoes, hair, makeup, etc.