I recently made a similar journey with my 2 year old and it took a substantial effort for both my wife and me to keep her occupied. We had plenty of her favorite toys and a video player to keep her occupied, but they were only minor distractions. Nobody slept for the entire journey.
Of course this may be a special case; there were other children on my flight that were only slightly fussy, but you should be prepared for the worst.
I agree that the newborn should not be a okay. If they don't have any problems with cabin pressure, you shouldn't have any issues. It is a good idea on takeoff and landing to have your kids either nursing or chewing on something to help with the pressure. Be sure to get an aisle seat, you will be getting up often.
Jet lag will make your children difficult to deal with when you arrive. Make sure to set aside time for naps, they are easy to overlook when traveling and visiting family, but don't let them sleep too long during the day or they won't sleep at night.