Read Deuteronomy 25:5 Using Other Translations
If brethren dwell together, and one of them die, and have no child, the wife of the dead shall not marry without unto a stranger: her husband's brother shall go in unto her, and take her to him to wife, and perform the duty of an husband's brother unto her.
"If brothers dwell together, and one of them dies and has no son, the wife of the dead man shall not be married outside the family to a stranger. Her husband's brother shall go in to her and take her as his wife and perform the duty of a husband's brother to her.
“If two brothers are living together on the same property and one of them dies without a son, his widow may not be married to anyone from outside the family. Instead, her husband’s brother should marry her and have intercourse with her to fulfill the duties of a brother-in-law.