Hi J.!
Carseats - when you check in at the airport, ask if it is a full flight. If it isn't, they may allow you to get extra seats for your two children. If so, you can bring the car seats with you past the gate and use them on the plane for your little ones. Otherwise, it's best to just check them at the ticket counter. No need to lug them around with yall to the gate if you don't need to. We've always had good luck when traveling with my daughter that we were able to get an extra seat for her.
Entertainment - Invest in a portable DVD player if you haven't already. Those videos on the plane will be essential, especially with them sitting in your lap. Take some books, toys, maybe something new for them that they haven't seen or played with previously.
Snacks - Take lots of snacks with you to help keep them settled and satisfied. Cheerios, mini vanilla wafers, teddy grahams, raisins, fruit cups, etc. will do the trick.
When going through Security, you will not be allowed to take any liquids with you unless they are in a 3.3 ounce or smaller container and all these items carrying on with you will need to be in a ziploc baggy and removed from your bags when you go through the screening. For the children, you can only take sippy cups of milk or formula. If you take water in their cups, they will dump it out (just experienced that last week).
I think that's about all my brain can remember for now. I'll add things as I remember them. Good luck and have fun! Get some rest before your flight, chances are you won't get to nap on the plane! :-)
And don't pack too too much. If you can, take a backpack (one for you and one for your husband), this should hold everything you need.
Take off and Landing - Give them a bottle or sippy cup to keep their jaws moving. This will help. My daughter has traveled a couple times domestically from here to San Diego but has flown three times from here to Finland, all when she was 5 months, 8 months, 11 months, 16 months, and 21 months). She does very well and the pressure has never really bothered her. But having something to drink or eat will help.
-Char