Marrying your brother-in-law

It seems that I am not the only one (Korean link) to surmise that my heroine Soseono's marriage to her second husband was a form of Levirate marriage where a man married his late brother's widow. The thing is, the relation between No. 1 and No. 2 stretched the definition of "family," to say nothing of "brothers."

( Of ancient power struggles and romantic comedy )