Please take your cats with you. I can highly recommend a Dr Karu in Jalan Loke Yew who can make all the arrangements to any country. His number is 012 3355655. He is helping me to take my 3 cats back to UK in June when I leave Malaysia. Please don't take any creature's life so lightly that you will just give them away and move on. I am sure they will miss you very very much :*(
Fiona, as Catpaw mentioned, have you looked into the possibility of taking your cats with you? It depends upon the country of course, but some countries' requirements aren't so overwhelming. It's a shame to re-home them if you don't have to. :-)
Why don't you take them with you? I have friends take their cats and dogs with them when they move to oversea. It's not good to have cats for a bit them let them go when are going abroad. You won't give your children away will you?