Hi there. This sounds like an infection caused by an organism caused 'Mycoplasma synoviae'- it settles out in joints and causes lameness, and also causes respiratory signs sometimes(hence the one with the eye infection).
You need to get an antibiotic called 'Tylosin' (Tylan), you will probably have to get it on prescription from your vet- treat all the affected birds, if any other birds start with it then inject them immediately with the Tylan.
Andrea
Bird Veterinarian
15 years in companion animal practise, BVM&S degree Edinburgh university