Animals don't have the ability to choose right and wrong like we do, and the other cat owners might not even know what is happening. That is such a rough situation. I am sorry to hear that your kittens have been hurt.

I don't know what to tell you about how to keep your cats safe, since they need to be outside. I'd like to build an outdoor enclosure (cat kennel) for my cats so that they can go outside. I'm not really sure what would be involved in doing that though. I am afraid to just let them out here because we live on a pretty big street, and I am afraid they wouldn't avoid the traffic.

Talking to the other cat owners would be the most direct approach, and probably the right thing to do, but that doesn't always work out well, especially when you are upset. Things can come out wrong, they could be defensive, etc. I'm not sure that I would be up to the task, not sure about you. I'd ask the vet for advice. Is there any chance that the vet might talk to the other cat owners either for you or with you?