@Crazielady420,
Buy some new toys they haven't seen before and that occupy them for a longer period of time. Engage them in lots of little conversations, singing songs etc. that always helps.
I remember our first transatlantic flight (16+ hours) when my daughter was around 4 years old. I was so anxious that she might act out and be bored
beyond tears, but I worried for nothing - she was perfectly fine, and talked
a lot to the passengers around her and watched her cartoons. I should have given her more credit....
Your girls will be fine too! Just make sure they don't get too much candy
or other sugary food items that make them hyper. As a emergency kit I always had some children's benadryl with me - never needed it but I felt
safer having it, just in case.