S.H.
with 9 years btwn my sons....& my sis having the same situation, we've always had fun with vacationing. We have found that by letting the little ones stay up a little later & the older ones having quiet activities to keep themselves entertained.....we had zero sleeping issues. :)
We have also split the parental duties. One adult at the pool late with the older kids....& the other adult in the room with the little ones. Most of my traveling was with my Mom &/or Sis. But the same method worked when my DH traveled with us too. Conquer & divide works wonders!
Good Luck & enjoy! You are creating a lifetime of memories!