1,574. Who is Considered to Have Fulfilled the Obligation to Procreate?
Hilchos Ishus 15:4
In order to fulfill the mitzvah to procreate, a man must father a boy and a girl. This is inferred from Genesis 5:2, “Male and female He created them.” If one of these two children is congenitally infertile, he has not yet fulfilled his obligation.
Hilchos Ishus 15:5
A man is considered to have fulfilled his obligation to procreate even if his children predecease him so long as they have left behind children. This is because grandchildren are considered like children. This is so when the grandchildren are both male and female, the offspring of a male child and a female child, even if the grandson is from his daughter and the granddaughter is from his son. Since they come from two of his children, he is considered to have fulfilled his obligation to procreate. However, if he had a son and a daughter who predeceased him and one of them left behind both a son and a daughter, the grandfather is not considered to have fulfilled the mitzvah of procreation.