I'm so sorry you don't have the FP for Anna and Elsa, but I'd like to share a couple of thoughts as I have been researching this for months for my autumn trip. I tried to book at 60 days out at midnight and could not get them, but I kept checking and was able to book for all of us. Try checking one at a time, and if you find anything on a day that works for you, take it. Then try to keep adding other family members and eventually you'll be able to overlap them. This strategy has worked for a lot of people. It does involve checking for FP frequently, but people do change their plans and cancel them sometimes.
Other option is to be at MK at rope drop, head straight to Anna-Elsa (make sure you know where you are going so you can be quick), and get in line. I've heard of waits less than 20 minutes with this strategy.
Good luck! I hope this works out for your family.