Is it permissible to propose to a girl whose foster mother is the sister of the suitor from his mother's side, knowing that the suitor's sister is the foster mother of the girl?

If the man's sister breastfeeds his female friend five full feedings, then it becomes forbidden for him to marry her, because she has become his sister's daughter through suckling. However, if the feedings are fewer than five, then it is not forbidden, and this is the most preponderant opinion.