I totally understand not wanting to pay for someone else's animals!!!!
But our policy (mine and hubby's) is to trap and have fixed any cat that is on our property. We could care less if the owners want the cat(s) spayed or neutered. If they felt strongly about it, they shouldn't let the cats out to begin with.
You can click on the SaveSamoa image in my signature line to help search for low-cost spay/neuter services. You can then go to the owners with that information. If they're unreceptive, make the rounds of the neighbors to take up a collection after you find out how much it will cost to have all of them fixed. Just let everyone know that they are just four cats now - but come Spring it with just one female in the bunch it may be nine. And if the Toms get any females you don't see pregnant, than number could easily more than double.
Besides - this also provides the service of educating your neighbors about the importance of spaying and neutering all animals.
If you want to go to your neighbors armed with info about spaying and neutering (has SO many health and behavior benefits (apart from just eliminating unwanted, homeless cats) - it eliminates the risk of certain types of cancer, eliminates most fighting, eliminates spraying, eliminates wailing and noise - and the list goes on....), you can use this link to print out info on it: http://www.cvm.umn.edu/vmc/forclient...rbenefits.html