suggestions needed on neglected cats

I need some sensible suggestions on how to tackle a problem I have with some neighbours who v regularly get new cats/kittens on a kind of rolling cycle . The cats are kept feral in the belief that they will catch enough mice to eat in the garden (there really aren't that many mice) so are left inevitably without sufficient food and shelter - this situation remains in place throughout the year come rain, frost or shine. The cats (currently there are three) unsurprisingly seek shelter and any other food they can scavenge in other people's gardens and sheds in the area. The cats never seem to be neutered and are likely not microchipped. Currently all the local tom cats have appeared to try their luck with an older female (which is currently in season) and a younger kitten has an eye infection which doesn't look to be getting better and is clearly causing it some distress. This is not the first injured cat that has been ignored by the 'owners' and others have inevitably also become pregnant. On one occasion a litter of kittens was found in the street outside the relevant house. The residents said they didn't want them. Thankfully a passerby who didn't live far away went to get a cat carrier and took them to the vets to re-home. But this is the kind of thing that it would be very good to stop. 

Any queries about clearly sick cats have been met with aggression by the owners in the past so I don't feel I can approach them again. The frequent replacements and therefore the welfare of the cats and their neglect is the only concern. If anyone has any workable suggestions to prevent this cycle of neglect please let me know.