I just sent an e-mail to my mother in law a few days ago with a wishlist that she requested, and I specifically put in there-no toys, please! =) We have the same problem- the only grandchild on both sides of the family, so everyone wants to get her stuff. So, this is what I did- I suggested kids CD's, educational DVD's, Precious Moments figurines (the number train so one could be added every year), and books. I figure you can't have too many books, and kids CD's, and they don't take up much room. If you need clothes for your girls you could ask for those specific items. I do that a lot, too, so I don't have to spend a bundle on clothes. The grandmas are ecstatic because they can go shopping, and I'm happy because I don't have to spend the money! Other ideas- what about everyone donating to a big item for your daughters? Something you would like them to have, but maybe wouldn't be able to afford otherwise, like a swingset, or a bike, or a trampoline. At least then they would have something really great, it would get used, and it wouldn't clutter up your house. If none of these ideas fly with your family, you may want to try rotating the toys. Keep a manageable amount out, and put the rest in a box for a month, and then rotate them. The kids will think it's Christmas all over again, everything will get played with, and you can still whittle things down when there gets to be too many toys again.
My sister-in-law has a big family, so they always draw names and set a limit of how much to spend. I've done the Toys For Tots- instead of exchanging a gift with a friend, my friend and I went together to the store to buy toys to give to Toys For Tots. We had a great time, didn't have to spend a ton, and we felt good about helping kids in need. Plus, we didn't have another knick-knack to dust! You could definitely do the same thing with any other charity you like. Ask for a gift to be given to Operation Christmas Child (you could even get together as a family to put the shoeboxes together- if you don't know what it is just ask me), or Samaritan's Purse, or Compassion International, or whatever other charity you like. I think you could just spread the word- just ask that instead of gifts, you'd like the money to go to "x". This is easy to ask for your gift to be substituted, but not as easy for your kids. Just say you've been really blessed and don't need anything, so you'd rather have whatever they were going to give to you to go to someone who really needs it. And you could say that if anyone else wants to do that, that you'd be happy to.
Many blessings to you!