Well here is my opinion, it was illigal to take the animals. However I can't say I wouldn't have done the same, it does sound like the cat is living at the aunts, and maybe legally could be considered hers. I know my sister in law has cats moving in on her all the time, some technically belong to other people, but once they find her house they tend to stay (much to her annoyance). If I lived in town I'd put id tags on my cats, or keep them inside, otherwise I would imagine they may move in w/ someone else or become a nuisances for my neighbors (who may think they are strays). (Ironically my sister in law has two cats (that she claims) and I never see them off her property even though they are outside).
These cats where clearly being neglected, and the neighbor doesn't seem to have any plans to change that. I'm sure there are other ways, but if those cats lived here they'd be doomed if no one took them in. The police here will not do anything, they have better things to do (ticket writing is so time consuming). The only thing you might do is call the dog pound who "might" come pick them up, I guess then you could adopt from them (and cats are free). The only other option I can see is trying to buy them from the current owner, but I'm sorry I'm not going to pay someone to be neglectful. I guess one other option would be to take the cat, have it spayed, and return it (also illigal, but in this case the neighbor probably would be happy), I wouldn't because again it's just a reward for the neighbor to be irrisponsible.
I think for people that do have options in these cases, it's just so hard to imagine it without any, and here there would be no help for these cats unless someone was willing to step in and "steal" them. Now I'm not saying the OP didn't have options, I don't know their area, but I know not everyone does.
