The last wedding I was in was the only wedding where the bride just let us wear our hair down like we normally do.
I think we all looked so good compared to other weddings we've been in where our hair is done in some do that we would never wear normally. I just blowdried it out, and put some velcro rollers in it so it had body. That's it!
I'm letting my girls decide what they want to do. I want them to feel comfortable and I think it would be hard to find a look that suits them all since they are so different. Plus I'm cheap, where I'm from, if you want your BM's hair done a certain way the bride usually pays for it, so I'm definitely not wanting to do that!
Have you discussed this with your girls? Maybe they can all agree on a style or help you find inspiration pics that they also like. Have you picked a dress yet? Sometimes that will give you some inspiration too. I think a flower could look cute with a short flirty dress.