Is it permissible to marry the son of a maternal uncle or the son of a maternal aunt, knowing that the mother of the fiancée was suckled three full times by the mother of the fiancé?

According to the majority of scholars, breastfeeding is not proven by the mother's testimony, except for the Hanbalis, who allow it under certain conditions. Even with the Hanbalis, there must be five known breastfeedings for the prohibition to spread. Assuming breastfeeding is proven, marriage to the children of the maternal uncle or paternal aunt is not prohibited, as the breastfeeding does not extend to them. However, proposing to an engaged woman is forbidden.