The only requirement is having done at least 1 overthrow per zone. They should spawn after this... Good luck

I’m not one hundred percent certain that all of the following is [u]required[/u] before you can unlock the [b]Dual Destiny[/b] Mission, but I would suggest you and your friend double check that both of you have done each of the following: • Completed all Missions of the Final Shape Campaign. • Completed the [b]Lost in the Light[/b] and [b]Found in the Dark[/b] post-Campaign Missions (or the [b]Home[/b], [b]Hollow[/b] and [b]Queens[/b] Adventures on second/third characters). • Completed all six Cysts within the Pale Heart. • Obtained the [b]Still Hunt[/b] Exotic. • Completed the [b]Excision[/b] Mission. If you both have done each of the previous items already, here are a few more things to try knocking out to see if anything changes: • Obtain the [b]Ergo Sum[/b] Exotic. • Obtain the [b]Khvostov[/b] Exotic. • Obtain the [b]Microcosm[/b] Exotic. • Defeat all nine Overthrow bosses (three per Overthrow zone). Note that I have personally [i]unlocked[/i] Dual Destiny and can confirm that clearing the Raid is [u]definitely not[/u] required. (΄◉◞౪◟◉｀)