call animal control. it is what is best and they wont tell them it was you who called, they wont even tell them they got a call at all.

it is a health hazard as i am sure the cats arent vaccinated nor spayed/nuetered, it is unfair to the cats and unfair to you.

they will pick them up and find them good home, or if they feel the people will comply with city laws and follow guidelines set out they will allow them to keep them.