What would you do? A little rant...

Hi. Please forigve me for using this forum to rant, but I would really appreciate some advice on how to handle this matter:

Me neighbors are starting to get on my nerves. They are a nice, retired couple, a little crazy, but we are on good terms. We live in the suburbs, and our houses are not far apart. The problem is that they feed the wildlife, including foxes, birds, and also feral cats. I have 3 outdoor cats, and lately there has been tension between my cats and the feral cats that seem to keep coming out of nowhere. Last week, my neighbors went on vacation, and the feral cats that they have been feeding started to come to my yard and harass my cats and stand outside my door, waiting for me to give them food. I didn't want to start taking care of more cats, but I didn't want the cats to go hungry either, so I fed them. I was very angry at the time, because I knew that once I started feeding them, they would keep coming back. I felt it was very irresponsible of my neighbors just to leave on vacation without arranging for someone to feed the cats. To me, it shows that they are not feeding the cats for humanitarian reasons, but because of the same reasons that they enjoy feeding the birds. To me, there is a big difference though.

Anyway, I arranged for my vet to come by and spay/neuter the new feral cats that have been coming to my yard almost everyday now. I'm also annoyed, because I feel that the neighbors should be helping to arrange and pay for the altering, but they just don't get it. We've spoken about the cats on numerous occasions, and I've tried explaining the situation to my neighbors, and hinted at all the time and costs involved in trapping and altering, and the stress it is giving to me and my cats, but they don't get the hints. I already see more new cats starting to congregate in my neighbor's yard, and I don't want these larger cats to run my own cats out of their territory. My cats are indoor/outdoor cats, because they were born feral, and they don't like to be inside for more than a few hours at a time. Therefore, I just can't keep them locked up inside.

I'm sure that my neighbors would be happy to have even more cats around. They are obviously not stepping up to take responsibility for these cats. They don't even try to socialize with them. All they do is walk outside once a day, dump some dry cat food into a plate, and go back inside and watch all the cats as they come. They are not even giving the cats enough food, just whetting their appetites, and that's probably why the cats are coming to my yard now. I don't mind feeding a few extra cats, but I really cannot afford to keep taking care of more cats, especially if more keep coming.

What would you do?