Getting them something personal is always nice. But I like the idea of getting them something they can use for the wedding or to help them out with the costs of being in the wedding. Giving them their jewlery to wear the day of the wedding is a nice one. As well as getting their hair done, helping off set the cost of the dress, or shoes.
I was recently in a wedding and the bride and her family paid for half our dresses. She also gave us tote bags, our jewlery, bath and body stuff, monogramed make up bags, our shoes, candle holder with candle, and one nights stay at the villa the night before the wedding as gifts.
I've also been in weddings where the gifts we were givin were not that big. Its what the bride and groom could afford. Its always nice to get something. Most of the times it was the jewlery we wore the day of the wedding. I've also in the past have gotten shot glasses, a flask (yes a flask), a journal, gift certificates and other things that were specific to me.
If I was you, I would try to get something like the jewlery to wear, and maybe something the is special to each individual. Its hard to get the same thing for everyone. You might be lucky and be able to do that though. Just stay within your budget. And remember, its the thought of the gift. Good luck.