IMO they would be a lot safer in a cattery for that amount of time, for someone to have them in their home could run the risk of escape (a good cattery should have facilities in place to stop this happening)
Settling in a new home with strange people wouldnt be much different to settling in a nice cattery. It would be worth a longer drive out of your area to get a nice one
Have you any pics of your kitties?
Oh, to rely on a catsitter for 4 weeks without having previously used them could be dodgy, some of them are lazy butter who dont change water fountains etc, ok for a weekend but not that long.