K.W.
Wear your infant. (You'll have to take infant out for takeoff/landing). Check the infant car seat.
Get a "go go kidz" attachment for the older kiddos carseat. Wheel the 2yo through the airport (use as a stroller). I'd gate check the car seat, which will leave a bit more room for you and the kiddos in the plane. Get a CARES harness for the 2yo if you can. The 2yo can carry/hold a small carryon bag with his/her stuff while riding in the carseat.
Bring snacks and extra clothing for 2yo, and a sippy cup. Bottle or breast for infant. You'll want both of them to be sipping liquid when the plane is ascending and descending.
Pay to check all extra luggage. You have enough to worry about.