Hey Richard
I'd suggest submitting some faeces to your local avian vet, they should be able to pick up if you have any worms in your collection. Will be good to get a baseline for what is going on. If your birds are in outdoor aviaries they probably do have worms. De-wormers depend on the type of worm usually (hence submitting the faeces). If your birds have tapeworms then they'll need praziquantal. If roundworms are a problem (such as capillaria) then Moxidectin is usually good however Capillaria are quite resistant to drugs and can be a nightmare to get rid of. Ascarids usually require a 5 day course of fenbendazole. For routine worming every three months is usually recommended and usually with Moxidectin however, you won't kill tapeworms and if ascarids are a big problem than moxidectin can do more harm than good. Moxi kills the worms off quickly and as ascarids are very big this can result in intestinal impactions and perforations. This is why fenbendazole is recommended as it kills the worms slower and over a longer period of time to give the bird a chance to compensate.
Not as simple as it seems, huh
My recommendation to my clients is to submit a pooled faecal from aviaries every three months to see what they need to deworm with. This is the safest and should be easy if you have an avian vet nearby.