Cat Ranch Population Control

My name is Kristie and I own a home in Lansing, Iowa. Last year, I noticed a pregnant feral cat on my property and I fed and sheltered her. That seemed to bring all the outdoor cats to my door.  At last count there were 12 cats, from 4 months to adult, coming around daily. I have been able to trap/spay/neuter 4 of them with the help of our local animal shelter and veterinarian service. When I called for additional financial help they said they needed to wait for additional donations and grant money. I told the cats not to breed but they aren't listening. All money raised will go towards TNR the remaining cats. Any excess would be donated back to the shelter. Thank you for any help you can give me is appreciated!!