Ok from what i have found, generally popeye is not fatal, but of course your fish will probably loose sight in that eye or loose the eye all together.
You think the fish also have an internal parasite?
Worms possibly is that right?
I will try to do some reseach on internal parasites to see what is recommended for ya

Have you tied medicated food for the internal parasites?
I am guessing it is something like skin or gill flukes, tell me more about the symtoms and what you have been using and i will try to find more info.
Thanks
Aimee