I put an update to my kitten post in the comments box after your replies, but there has been a further development.
The kitten lady has just rung to say that she met two people from the caravan site just below the farm and they said they would keep an eye on the kitten traps for her. They have just rung to tell her that one trap has caught both kittens and they have eaten the cat food in the trap and are curled up together asleep. She is on her way to collect them.
All's well that ends well and all six are in safe hands.