i would suggest asking a few neighbors that you know like the chickens to write a letter stating that they aren't a problem. make sure they include where they live in relation to you and how long they have lived there. you don't really need to do anything with these letters now, but they would be nice to have on hand for future reference if it comes to that.
you might also ask the nice elderly couple to contact whoever it is at the police department, etc, that you have been dealing with. i can understand their hesitance in giving out the information to someone involved, but if you explain that you are being harassed and are afraid for the safety of your chickens and child, they may be willing to tell the police what they know. the police won't get involved for slander, but they will get involved if this person is encouraging people to falsify claims/evidence. that is illegal.
good luck.