Siman 14

The Tur wrote: It is forbidden for a person to perform erusin within thirty days of mourning, and one who has small children and has no one to serve him—it is permitted to enter into marriage even within seven, however, he may not have relations with her until after thirty days. And one who does not have children or who has not yet fulfilled the commandment of procreation is forbidden to enter into marriage within seven, but after seven it is permitted to enter into marriage and have relations even if he is mourning for his father or for his mother. And after thirty days, any person is permitted even if he fulfilled the commandment of procreation and does not have small children, even if he is mourning for his father or for his mother. Thus far his words. And the Rambam permits performing erusin even on the day of death, provided that he does not make a feast, as is written in Yoreh Deah siman 392.

If one betrothed a woman and she became a mourner, and he has not fulfilled the commandment of procreation—it is permitted to marry her within the thirty days of her mourning [Tur], but if he has fulfilled the commandment of procreation—he must wait until after the days of her mourning. And regarding betrothal—it is permitted in any case, provided that he does not make a feast, and in Yoreh Deah there several more laws regarding this were explained; see there.