We have been traveling with our boy girl twins since they were about eight weeks old. Our first airplane trip was on a corporate jet and just made things easier. We have since taken several trips via plane since then. When they were younger, we actually had them as lap babies since it was easier. I believe we also got a third seat and brought a car-seat onto the plane and switched them out accordingly as we needed to. The good thing is that having both my wife and I on the plane, made it easier to tag team the children. The other thing we noticed is that if we work it just right, both kids fall asleep shortly after take off and sleep to the hum of the engines. Hope this helps in some way and hope to meet another twins dad here in Omaha for the convention.

Be ready to change diapers in extremely tight quarters (there was no changing table in the airplane bathroom and virtually no where to change him except on the closed toilet seat). Also bring at least one change of cloths for everyone. On the way out, our son pooped twice. While waiting in line to change him, one passenger plugged their nose and said "oh jesus". On the way back, our son also pooped. He got ahold of the dirty diaper and threw it on the floor making a mess. While in our seats, he threw up all over himself, my wife, and me. He wouldn't sleep for more than a half our either way so bring lots for them to do. We upgraded to economy plus on the way back so he had some room to play on the floor (this was a great decision). This flight was probably about as bad as it gets and if I knew then what I know now, I would probably try a nighttime flight, upgrade to economy plus, and hope he sleeps.

Do Not Be In A Hurry.
Pay for the extra seats.
If it's a long flight, we give our daughter baby tylenol before leaving the house. Have some with you in case the pressure hurts their ears.
Allow for plenty of time at security.
Bring the car seats (the kids know what's expected of them in a car seat) and strollers (check them at the gate)
If you have a fold up two wheeled dolly that's light enough and small enough, use it to transport the car seats.
Have snacks and drinks (presealed 4oz max.) for the pressure changes. (we had to pour out a bottle of breast milk)
I usually board first and get the car seat set up, my wife and kid board at the last boarding call.
We usually sit in the last row. It puts us closer to the restroom; It gives us extra time to pack up; it allows the other passengers to get out of the way (bumping other passengers heads with our car seat taught me this lesson); and it sort of isolates us if our daughter starts to act up.
Bring in flight distractions. We use a portable DVD player in addition to games and toys.
Try and maintain your good humor.
Good luck.

All of what is said above is great advice. Allowing yourselft plenty of time to get to the gate and settled is of utmost importance.

One other thing specific to twins my wife and I found out is this. (I have 2 boys) Each row of 3 seats only has 4 oxygen masks. So, if you only purchased 2 seats for 2 lap babies in the same row that's 5 people in a row (you, your wife, the other person in seat 3 and your 2 kids). With only 4 masks they won't let you sit together. No fear, there are solutions. 1st choice is just book the whole row... having an extra seat to change diapers, set kids in whatever sure would be nice. If thats too much $$$, book your seats across the isle from each other so you won't have to be moved...potentially several rows apart.

I'd also prep your bottles, sippy cups whatever they drink BEFORE you get on the plane. Trust me, you want those puppies ready when you need em.

Overall, as long as you've got most of your ducks in a row you'll do fine. My wife says "dress em cute and let em make friends before the plane takes off" Good luck to you!