Wow that will be an adjustment for them at first. Moving, air travel, new home, apartment lifeā¦ I have been told that a cat's memory lasts about a month. If that is true, maybe you will only have a few weeks of upset to appease. Your cats are beautiful; I could never part with them.
Get some cat towers and make the inside fun and exciting for them. I have 3 towers for my cats and they love one that is 7 feet tall and one cat ops to play on it even when the patio door is open. I just ordered another climbing pole that I plan to attach to the wall so they can go from the tower up to a triangular opening in the wall that starts at about 8 feet and goes to the ceiling. I see them looking up there wondering how they can explore it.
There are all sorts of sites but this one is my favorite for cat furniture:
http://www.catsplay.com