Well, invite them over for tea, and show them your set up , explaining how much time it takes you to clean it, and how important it is for the birds health and well being it is to keep things clean.
If that doesn't work, hit them on the head with Babs' flying frying pan , look them in the eye with your best border collie star and say: YOUR BIRD CAGES ARE FILTHY!!! GO HOME AND CLEAN THEM, OR YOU'LL GET ANOTHER SMACK UP THE SIDE OF THE HEAD!!!
One of these methods, should work...
