If she takes control of a neutral character or a Night's Watch character if its a unique character does she take control of it if there are dupes on it? Or can you discard a dupe to save the character from being controlled?

Duplicates can only be used to save a character from being removed from play. Taking control of a character does not remove it from play, so duplicates cannot stop someone from taking control of your unique characters.

It is mentioned in the FAQ that when an effect takes control of a unique character, all duplicates on that character change control, too.

Attachments on the character stay controlled by the same player as before, though (each card is controlled independently).

Ok I was wondering, if you blank Ygritte do you get control of your character back then?

No. Once her ability is triggered, the effect lasts for the duration of the effect specified in the effect. Blanking her text will not end that duration early.

What does happen in this scenario?

With my ygritte (Y1) I take control of my opponent's carrion bird.

Then my opponent plays Ygritte (Y2) and retake control of carrion bird I have stolen.

Then I manage to kill my opponent's ygritte (Y2).

What happens to the poor bird???

It goes back to the last person who controlled it.

With "take control" effects, the last one applied is the one that matters. But it doesn't end any of the previous ones. They essentially form a "line" with the character being controlled by the guy at the front of the line. When the guy at the front drops out of line, control goes to the guy who was next in line, and so forth - back to the owner.

What happens if it is the other way around - Ygritte (Y1) gets killed before Ygritte (Y2)

When Y2 gets killed does control revert to the Y1 player and then immediately back to the Y2 player?

This could also be in a melee game - so:

Player A - plays Ygritte and takes control of a character (C1) (from player C)

Player B - takes control of C1 from player A ... e.g with a seductive promise

Player A's Ygritte gets killed

Presumably Player B keeps control of C1 until something else changes?

When Y2 gets killed does control revert to the Y1 player and then immediately back to the Y2 player?

No. The Y1 player has no active "take control" effects, so there is nothing to re-assert itself when Y2 dies.

Using the "next in line" metaphor above, the Y1 player dropped out of line before the Y2 player did. So the Y1 player is no longer the "next in line" when Y2 drops out. Control goes immediately to whomever Y1 took the character from in the first place.

Presumably Player B keeps control of C1 until something else changes?

Well, that's going to happen anyway in your example because Seductive Promise doesn't have a duration, and thus will never "drop out of line" before the character leaves play.