Can't find the thread I thought was here. Question is do dupes help out are they all killed before end of phase when Poison goes.

At the end of the phase, remove the poison token and kill a character.

The card does not prevent them being saved, so a dupe or bodyguard or something similar can still be used.

Duplicates can save from any effect that would cause the card to leave play, provided the effect does not say "cannot be saved" or isn't going to instantly re-apply itself to drive the character from play (Dracarys, for instance).

Tears of Lys is a one-time kill at the end of the phase. You can use a duplicate (or bodyguard, or Aemon, etc) to save from it.

I've had someone try to double Tyrs my Robert Baratheon duped (by use of second intrigue challenge). Is this a thing? Does one poison counter destroy the dupe, and the second kills him?

Functionally, yes. In the nitty gritty, each Tears effect tries to kill him once. You can save him (or not save him) from each. Since you only have one dupe, he'll be dead by the end of both delayed effects anyway, but technically you could choose to let him die to the first instead of the second (changing nothing, of course, to the end game state - but you're not forced to use that dupe)