Awesome - thanks for the replies. I have got already got a quote from a couple of pet travel agencies but staying with my sick parents till we find somewhere of our own and they hate cats so exploring other options!!
Will look into the long term fostering options and ring a couple of shelters, I like this idea best as I am worried if we rent them out with the house and then the tenants plans change that I'll have to try and find a home for the cats from overseas which will be more tricky.
Also looked into cattery options but there's not much of a long term discount so really expensive!!!
By the way We're moving to the UK, was worried about quarantine coming back into Australia so good to know the rules are changing!