Will the foster mother's daughter become a sister to her sister's son through fosterage if her mother breastfed him two or three times 40 years ago, and is their marriage, which took place 22 years ago, valid?

If there is doubt about the existence of breastfeeding or the number of prohibited breastfeedings, the prohibition is not established, because the default is its non-existence. The default is not removed merely by doubt. The prohibited breastfeeding consists of five breastfeedings within two years, according to the more preponderant opinion. Therefore, there is no objection to marrying her daughter to her sister's son.