What is the degree of kinship that resulted after suckling between the two sisters and their children, and what is the ruling of Islamic law on that?

It appears that you and your sister each gave birth to a boy and a girl. Each of you breastfed the other's daughter, and your sister breastfed your son, but you did not breastfeed her son. This breastfeeding is permissible, and as a result, the boys who were breastfed by either of you become mahram (unmarriageable kin) to her daughters and her husband's daughters. The girls who were breastfed become foster sisters to the sons of the wet nurse. As for your sister's son, whom you did not breastfeed, he is a stranger to your daughters, and the ruling of his sister's breastfeeding does not extend to him, except for whoever was breastfed by his mother, in which case he becomes mahram to her. The breastfeeding that is recognized by Islamic law consists of five breastfeedings, according to the preponderant opinion.