In The Twilight world, male vampires have to mate with a human female to have a child. But that will end in tragedy for the human female's death, if the male vampire acts swiftly they can save both the child and mother.
Two vampires cannot have children, for example a female vampire and a male vampire cannot have children due to the female cannot carry a growing child, due to the fact that there bodies will not be longer to be able to gestate a baby full term, due to the fact that their bodies are frozen at the time of their transformation. They must either adopt children or turn a human at a proper age to do so.
Plus in the Twilight saga there are immortal children.
vampires can't have children because their bodies are frozen and can't change form. If the body is frozen for a female it would be frozen for a male so he doesn't produce anything. And for humans male vampires can produce sperm and ejaculate on each others buuttss so they can make the human female pregnant.