"The easy and humane thing to do would be to call the local animal control officer. Most communities have lease laws and they do include cats. What communities don't have a lease control ordinance do usually have a nuisance animal ordinance.
A cat is still a pet and the owner is still responsible for the critter.
Don't worry about the cats owners any more than they worry about you."
Nah, that's the wrong thing to do in my opinion. Just go talk to the neighbors and tell them of the problems you are having. Give them a chance to fix the problem first before you go to the authorities. That would be the neighborly thing to do. If they tell you to get lost or are unconcerned then do what you have to do. Believe it or not, neighbors have been working out little problems like this for many years before there were animal control officers.
There's a good chance that the cats owners don't even know where they are spending the afternoons. About the only way to keep a cat outdoors and in your own yard is to put it in a cage and then you'ld get busted for animal cruelty. You're damned if you do and damned if you don't.
Tony