ED quest

[Imminent]

Q> Regarding the nydhoggur quest, must I  finish the instance before I open the vengeful eremes gates? Also, do I have to finish Endless tower per character or 1 character unlocks the Endless Tower requirement for the whole account?

Yes and yes. You just have to finish nydhoggur quest and endless tower at least once and after that you could open vengeful's barricade with any character of the same account

it count on char not all acount

it should work with all characters on the same account. I have around 3 accounts that finished both nydhoggur quest and endless tower and each character is able to open the barricade without any issues. Do take note that only one character of each account finished the quests. I'm not sure if there was any change made regarding this but mine still works and I've actually just done ED two hours ago