when did you last treat them with ivermec? was it when you had them off me?
if so you could treat them with ivermec again you can use the ivemec with the xenex x
Parasites are species specific - cat's flies can't survive on guinea pigs, as little as on humans!
If your guinea pigs itch, they have guinea pig specific parasites, most likely mange mites which you can't see from the naked eye.
Please have your piggies seen by a vet before you try any more treatments to make sure that you treat them right!
dont worry hun does their skin look sore? can you see anything wriggling around in their hair? to surggest lice