My chickens had roundworm, but I only knew that b/c I took a fecal to the vet. You could do the same; take a fecal to be tested to be sure what kind of worms they have and then treat it accordingly. I used Wazine, but be sure you only use it for 1 day. I found that out the hard way. You cannot eat the eggs while treating w/this product, however.
I try to keep ever thing natural by put garlic and Apple cider vinager in the drinking water. In the summer we grow pumkins and give them to the chickens to eat. Both of these will help keep worms a bay natural but will not get rid of them.