Dating your sisters husbands brother
So a man whose wife produced only daughters, then the wife died, marries her sister and has a son, but his brother wants the title/land so challenges the marriage.The second most likely to challenge would probably be the husband himself if neither wife produced an heir. This would also work if Alice and Carol were sisters, and Bob and Dan were brothers.
Anyway, in 1835, Lyndhurst, concerned that the Duke of Beaufort’s heir could be stripped of his legitimacy, all his rights and his entitlements as heir to the dukedom if someone like Wellington challenged Beaufort’s marriage to his dead wife’s half sister, took the matter to Parliament in the form of a bill to legitimize the marriage. What eventuated was the bill that decreed that all voidable marriages performed before 31 August 1835, if not already voided, would be declared fully legitimate and all marriages within the prohibited degrees performed after that date would be void, invalid from the beginning whether challenged or not.Then Alice would marry one brother, and Carol would marry the other. In other words, it's any time a pair of siblings marry another pair of siblings.Someone marries the sibling of their own sibling's spouse. Or if the weddings don't take place at roughly the same time, the first wedding provided the ideal opportunity for the second couple to get to know each other.The figure that carried the full weight of these ideological struggles was the adult unmarried sister living in a married sister’s household; the specific issue upon which the English people focused was whether a man’s wife’s sister was, in law, the equivalent of his blood sister and therefore never to be his wife, or his metaphorical sister only and therefore an ‘indifferent person’ whom he could marry.” (Anne D.Wallace, “On the Deceased Wife’s Sister Controversy, 1835-1907″) one.