Identical twins are totally random events, and fraternal twins are only genetic from the pregnant woman's side of the family. If your mom was a fraternal twin, or if her mom or dad was, you might have an increased chance to have fraternal twins. But if your twins are identical, that just happened by chance. And nothing about your sexual partner's family would dictate twins. (Fraternal twins come from the woman popping out two eggs in a given ovulation, a tendency that she might have inherited from further up her own bloodline. But again, not from the twins' dad.)
Have you had any ultrasounds, and if so, how early in the pregnancy were they? What is your due date? Did it come from your doctor?