There is generally some confusion about twins running in a family. The tendency to produce more than one egg per cycle is an inherited trait . This trait is carried by the female, so twins might be predicted if the females on the mother's side of the family have had fraternal twins. The father and his family do not enter into the equation. Identical and conjoined twins have little if any genetic predictability.
Identical twins are one egg cell fertilized by one sperm cell.
The resulting zygote splits in the early stages and develops into two genetically identical individuals. Conjoined twins usually form in the same way as identical twins, except the zygote does not completely split. Conjoined twins will share some body parts. Describe the placenta. Count back 3 calendar months from the first day of the last period - then add one year and one week.