There could be many things wrong with these birds; I would not jump on this guy and individual breeds because you've had a slight problem, the first could have actually hurt itself like the vet said, the second and third could have been egg bound, so please do not jump on individual breeders, I'm sure if he intentionally sold you birds to die, they'd be dead by now.
Some breeders also do not vaccinate because of homoepathic practices.
Once an animal leaves his property he cannot be held for anything that goes wrong unless stated; Its been over a year since you've had them you said, so I doubt he has much to do with it.