Irresponsible pet owners

For the second time in 6 months, my house is a maternity ward for my irresponsible neighbors pregnant cat. In late September one of their 4 un-neutered females gave birth to 5 kittens in my bedroom closet. Knowing that they do not feed, innoculate or otherwise care for these poor cats, I was able to keep the "births" a secret and waited the 2 months and took them to the local animal shelter...where I was charged 150.00 to drop them off (they were consodered mine since I had been feeding them for 4 or more days...) (city law...they don't tell you this prior to you bringing them in...). These idiot "owners" (term used in loosest sense) never even questioned the absence of the cat...I heard them say thru the grapevine (literally) that they used to have 4 cats, but one ran away....

These people are renters who rent from a co. who will only take complaints about their tenants via written letter. I did that...no response. These people are not "approachable" about this situation and I suspect drug activity etc. etc.

My city has no laws regarding pet neutering...the animal control says they are powerless to do anything as they haven't broken any laws.

I have two neutered older male cats of my own who do not stray. These peoples cats are constantly running into my house to eat as they are basically starving. They provide NO shelter for them in the rain. I have created a monster by taking pity on these creatures and feeding them and obviously they aren't about to go anywhere.

Every cat rescue org. I contact will only take them if I pay for neutering. They aren't even MY cats...yet I am breaking a law if I do something about the situation. This latest group of soon to be born kittens will cost me a fortune. The other remaining females will be pregnant in no time, if they aren't already. Then the cycle starts all over again...

I am livid about this situation because these people don't care that they are breeding unwanted kittens, they are "thugs" to put it bluntly and I KNOW they will retalliate if I make a to do over this. Quite the conundrum...

I am not a millionaire and my patience is wearing very thin. I would never consider taking them and dumping them...yet I am stymied as to what to do.

Any ideas would be immensely appreciated...

Once again, the irresponsible get off scott free and the responsible ones pay the price...