Peas most likely don't get tapeworms that I have seen and if they did you will see it in the poop just like you will see roundworms in the poop except tapeworms are flat and they look like they are waving to you. You find a lot of tapeworms in fishtanks. Here is a post from Chickenzoo from 2011:
If they are 2 years old and have only been wormed with Wazine ( kills only round worms), then it is highly possible that they have another type of worm other than tapes, as tapes are not as likely. I worm with Safeguard liquid goat wormer at 1cc down the throat of adult peafowl (10lbs) . If they are really bad off I would start with 1/4 - 1/2 cc, wait 5 days then give the other as large worm die off at once can kill the bird. Ivomectrian applied to the skin at 1/2 - 1 cc per adult is also used 6 months after the Safeguard, but I would not use it on a very sick bird as in your case now. Blackhead as stated above is possible, you would see increased thirst, pecking at food but not eating, loss of weight and bright mustard poo. A fish med called Fishzole given for 5 days at 250mg 2x daily is the cure if caught in time.
I use safe guard at 3 cc/ml per gallon of water for 3 days and repeat in 14 then I use Ivermectin pour on for cattle I squirt 1cc on the skin at base of neck, doing this the birds get about a 1/2 cc being absorbed into the skin. Doing this twice a year and your birds should be worm free.