We had a similar story years ago. We contacted The Shamrock Foundation and they paid for the neutering/fixing of the kittens, gave us a big bag of food and two bowls to feed them. They said it was better to bring them back to familiar surroundings. They ended up coming into our house and liked it, but they always wanted out too. They were very special to us.
Thanks for doing your part in helping this cirlce of life pattern to end. If only more would help.