Neem oil can be toxic to some animals (like cats) and probably won't help you much toward your goal. It may change the natural ecology in your yard temporarily. Do you really want to do that?
Can you ask yourself why you feel like you have to eliminate tapeworms and their hosts? There comes a time when the effort, stress, cost and toxicity may make all of that not worth it. Tapeworms in their final hosts (those you find the adult worms in) are generally harmless. They're gross, sure. But are they really hurting anything? Will treating your flock for them make them healthier? I think that scenario is pretty rare.
I am not saying they're always harmless, but in general, I certainly don't worry about them in my chickens. I'll treat my chickens with a high-ish dose of fenbendazole if I suspect ascaridia and that will take care of other nematodes and tapeworms, but otherwise, I am not all that concerned with others.
Just my two cents.