For learning more about feral cats, how to do TNR, socialize the more tame ones, and return the more feral cats to their colony to be cared for, I highly recommend watching TinyKittens HQ on Youtube. It is a non-profit organization run by Shelly Roche in BC, Canada. They do NOT euthanize cats or kittens simply because they're feral, as PETA does. They spay and neuter all the adults and kittens, they socialize the kittens to get them ready for adoption, and if some of the adult cats are amenable to human contact, they socialize and adopt them out also. The more feral ones who want no human contact are returned to their colonies, and fed/watered and visited daily by Tiny Kittens volunteers.
All the cats/ kittens who come into TK are given the necessary vaccines, shots, medical procedures, flea/dewormer, etc.