E.,
First of let me say you are a brave woman! Also,I do have a few suggestions. I am really strict about gum and never let my kids chew it, yes even the 8 yr old. But, when we flew to Disney we let her chew gum as it did help her ears quite a bit on the plane. My son was less than a yr old at the time so all we could do for him was give him the bottle to suck on which we were told would help.
Another idea is to buy some cool tactile things they can do with their hands and not let them see them until they go on the trip. That keeps them more intrigued than just packing old toys. One of my personal faves is Color Wonder markers and coloring books. Silly Putty is also cool if your youngest won't eat it and drawing boards with the attached "pen" can be found in smaller sizes.
Find out exactly how many pieces of luggage you can bring with your children. I think a diaper bag is allowed and does not count as a piece of luggage but double check. I had a separated bag of just snacks, games etc. (Definetly bring snacks!!)
Be careful with the amount of liquid you pack with the new laws. Trust your instincts as far as bringing medication. Maybe you could just bring Tylenol. I am sure they have places you could buy it at if you needed to.
Couple more things, I suppose it depends on your flight, no guarantees... but our flight to Disney was full of kids and families so it was a little less stressful and in the end there was no crisis other than me walking up and down the aisles to comfort my crying infant. The worse thing that could happen would be that one of the kids would scream or bump into soemone's seat. Oh well, if it happens, it happens.
Lastly, expect some things will go awry but it doesn't have to ruin your trip. We had a great time even though it wasn't perfect. The goal is family time together in a change of scenery and you will have that!!!!
Have fun.
M.