Hello, this is Dr. Linda & thanks for contacting JustAnswer. I hope I can assist with your concerns today.
The answer to all of your questions is a big NO. Needles should never, ever be used more than one time, & the veterinarian contaminated his vial by introducing a dirty needle into it.
Most likely your GPs will be fine, but if any of them develops a swelling or abscess where the injection was given, I definitely would find another veterinarian to treat them.
You can also file a complaint with the state veterinary medical board if you want to go that far.
Please continue with any additional questions or concerns you may have.