In a pet store the birds will often have missing feathers. Many times the cage will have too many birds in it, making the birds argue about who is the chief. A few missing feathers is nothing to worry about. They will grow back unless the bird has been picked on so much that the skin is permanently damaged. It is recommended that you not keep a bird as a single pet.
Zebras are colony birds.
They like the company of other Zebras. The most common is to have one male and one female. In a pet store it is usually not know if the birds are related. If you are going to have your birds simply as pets, then it is not too important to have unrelated birds. If you want to breed your birds then they should be unrelated if possible.