Congratulations on your upcoming vacation. I would suggest that you check ahead of time and find out when the parades are -maybe MK the first day and Chef Mickeys.
If your DDs like to dress up, purchase items likethe glittery hairspray , makeup, Disney barettes, Tinkerbell/Princess pony holders at home and pack in your checked bag. This way they can have the Bippety Boppity experience without the cost. We've packed a pink polo type dress for our 4 yr. gdaughter and do her makeup/hair in the room and she feels like a princess.
In order to help with souveniers, we tell our gkids that we look the first 3 days and then buy the day before we come home. I also pick up small items from the dollar store (stickers, new toothbrushes, colors, Disney yoyos, etc.) and Tinkerbell will either leave these in the room or put them in the back pack to be handed out for using good manners and being patient. This helps to have money for one or two nice souveniers. Also, consider getting autograph books at home from dollar store rather than buying at WDW.
Since you will have rental car, stop at
Walmart/Publix and pick up snacks/drinks and some breakfast items to eat in the room.
Remember to slow down and enjoy the experience because you won't be able to see and do it all the first trip. After the trip, make a scrap book with each of your girls and then relive the magic over again.