From experience, putting them in their carry cage thingmajigs hungry is a good start. Once in the new gaff shut all windows and outside exits, then let them out for a mooch. Leave them to wander but put a cat plop box down. Leave them be for an hour or longer, then feed them. If you get a decent day, put them in their catcage doo dah and leave them by the open back door, that way they're safe but get a wiff of the new outside world. Repeat for a few days and release. They'll be fine I reckon.